May in the low desert

watering | what to plant | pruning | fertilization | problems

The spring blooming season is coming to an end as the temperatures begin to increase and the impending summer is fast approaching. Many spring-blooming annual wildflowers have expired and gone to seed. You can collect the seed and store in paper bags until fall or allow plants to reseed in the landscape. Rake up the departed annuals or cut back rather than pulling from the ground. By doing this, you will not disturb the soil and will allow the remaining root system to decompose.

Leaves of the Boojum Tree (Fouquieria columnaris) and Elephant Tree (Pachycormus discolor) will continue to yellow and drop. The Boojum Tree and Elephant Tree are summer-dormant. Periods of active growth begin from about November through May. When the leaves of both succulents begin to drop, less water is needed.  See our Desert Gardening Guide on the Boojum Tree for more information on caring for this bizarre succulent.

Many other winter-growing succulents including Live Forever (Dudleya saxosa ssp. collomiae), Succulent Geraniums (Pelargonium spp.), Iceplants (Malephora spp., Drosanthemum spp., Cephalophyllum spp.), Living Stones (Lithops spp.) and crassulaceous plants (Kalanchoe spp., Cotyledon spp., Echeveria spp.) will also begin to drop their leaves or shrink in size. These summer-dormant succulents need to be watered less during the summer months.

The iconic Saguaro (Carnegiea gigantea) and the majestic Ironwood (Olneya tesota) will be blooming. The Saguaro flowers open in the evening and will remain open throughout the following day. Many animals and insects are attracted to the white, fruit-scented flowers. The Ironwood will produce blush pink to white, pea-like flowers that are also sweetly scented and attractive to many animals and insects.

Many Elephant Trees (Bursera spp.) will be producing new leaves throughout the warm months. If damaged by a previous frost, wait until new leaves appear before pruning.

Karoo Roses (Adenium spp.) should be “waking” from their winter dormancy. Leaves and flowers should start appearing on the succulent stems. You can water and fertilize your Karoo Rose throughout the warm season. For more information on caring for your Karoo Rose see our Desert Gardening Guide.

Other winter-dormant succulents that should be exhibiting renewed growth with increasingly warmer weather include:  Limberbushes (Jatropha spp., Uncarina spp., Pachypodium spp., Fockea spp., Adenia spp., Cyphostemma juttae), Carrion Flower (Stapelia spp.), Madagascar-ocotillo (Alluaudia procera), and Globeberries (Ibervillea spp.). Allow your succulent plants to produce new stems and/or leaves to determine whether or not any pruning of frost damaged stems will be needed. Regular and careful watering can resume for many of these warm-season growing succulents.

Plant your Ocotillo (Fouquieria splendens) from March through May as these are the ideal months to achieve greater transplanting success. For more information on planting an Ocotillo see our Desert Gardening Guide on planting a Bare Root Ocotillo.

Look for signs of water stress exhibited in cacti and warm-season growing succulents. A few symptoms to look for include:  shriveled or shrinking stems and/or leaves, pale green to yellow epidermis (skin) and in the case of many Prickly-pears (Opuntia spp.), wilted or limp stems and fallen pads. See the watering section below to find out how to water your cacti and warm-season growing succulent plants.  Keep in mind there are winter-growing succulents that can exhibit the signs of water stress, but are actually going dormant for the summer season. It is imperative you do not overwater these winter-growing succulents during this time.

Would you like to remove your Bermuda grass lawn?  The hot summer months are the best times to begin treatment for eradicating Bermuda grass. For more information check out our Desert Gardening Guide on Bermuda Grass Removal.

If you have not applied organic mulch to your vegetable and herb beds, now is the time to do so. Applying a layer of composted mulch can help conserve moisture thus requiring less watering during the summer months.

Blooming herbaceous perennials, groundcovers and vines can include:
• Chocolate Flower (Berlandiera lyrata)
• Desert Milkweed (Asclepias subulata)
• Pineleaf Milkweed (Asclepias linaria)
• Desert Marigold (Baileya multiradiata)
• Paperflower (Psilostrophe cooperi)
• Desert Senna (Senna covesii)
• Arizona Foldwing (Dicliptera resupinata)
• Dogweed (Thymophylla pentachaeta)
• Gaura (Gaura lindheimeri)
• Mexican Hat (Ratibida columnifera)
• Desert Four O’clock (Mirabilis multiflora)
• Sacred Datura (Datura wrightii)
• Yerba Mansa (Anemopsis californica)
• Trailing Lantana (Lantana montevidensis)
• Blanket Flower (Gaillardia pulchella)
• Bloodflower (Asclepias curassavica)
• Desert Verbena (Glandularia gooddingii)
• Marvel of Peru (Mirabilis jalapa)
• Yellow Dots (Sphagneticola trilobata)
• Coral Fountain (Russelia equisetiformis)
• Plumbago (Plumbago scandens)
• White Woolly Twintip (Stemodia durantifolia)
• Mealy-cup Sage (Salvia farinacea)
• Damianita (Chrysactinia mexicana)
• Desert Zinnia (Zinnia acerosa)
Blooming vines can include:
• Queen’s Wreath (Antigonon leptopus)
• Arizona Grape Ivy (Cissus trifoliata)
• Yuca (Merremia aurea)
• Yellow Orchid-vine (Callaeum macropterum)
• Passionflowers (Passiflora spp.)
• Old Man’s Beard (Clematis drummondii)
• Snapdragon-vine (Maurandella antirrhiniflora)
Blooming shrubs can include:
• Fern Acacia (Acaciella angustissima syn. Acacia angustissima)
• Oreganillo (Aloysia wrightii)
• Beebrush (Aloysia gratissima)
• Flame Anisacanthus (Anisacanthus quadrifidus var. wrightii)
• Woolly Butterfly Bush (Buddleja marrubiifolia)
• Showy Menodora (Menodora longiflora)
• Baja Fairy Duster (Calliandra californica)
• Desert Ruellia (Ruellia peninsularis)
• Pink Fairy Duster (Calliandra eriophylla)
• Tree Ocotillo (Fouquieria macdougalii)
• Little-leaf Cordia (Cordia parvifolia)
• Silver Dalea (Dalea bicolor)
• San Marcos Hibiscus (Gossypium harknessii)
• Yellow Bells (Tecoma spp.)
• Sky Flower (Duranta erecta)
• Red Bird of Paradise (Caesalpinia pulcherrima)
• Sugar Sumac (Rhus ovata)
• Guayacán (Guaiacum coulteri)
• Fire Bush (Hamelia patens)
• Graythorn (Ziziphus obtusifolia)
• Flattop Buckwheat (Eriogonum fasciculatum)
• Bush Germander (Teucrium fruticans)
• Mexican-honeysuckle (Justicia spicigera)
• Mexican-oregano (Lippia graveolens)
• Sweet Almond Verbena (Aloysia virgata)
• Silver Nightshade (Solanum hindsianum)
• Turk’s Cap (Malvaviscus arboreus var. drummondii)
• Rock-rose (Pavonia lasiopetala)
• Mexican Oregano (Poliomintha maderensis)
• Arizona Rosewood (Vauquelinia californica)
Blooming trees can include:
• Ironwood (Olneya tesota)
• Catclaw Acacia (Senegalia greggii  syn. Acacia greggii)
• Crucifixion Thorn (Canotia holacantha)
• Desert-willow (Chilopsis linearis)
• Bitterleaf Condalia (Condalia globosa)
• Kidneywood (Eysenhardtia orthocarpa)
• Screwbean Mesquite (Prosopis pubescens)
• Palo Blanco (Lysiloma candidum)
• Texas-olive (Cordia boissieri)
• Honey Mesquite (Prosopis glandulosa)
• Velvet Mesquite (Prosopis velutina)
• Whitethorn Acacia (Vachellia constricta syn. Acacia constricta)
• Smoke Tree (Psorothamnus spinosus)
• Texas Ebony (Ebenopsis ebano)
• Golden Leadball Tree (Leucaena retusa).
Blooming cacti and succulents can include:
• Saguaro (Carnegiea gigantea)
• Horse Crippler (Echinocactus texensis)
• Engelmann’s Hedgehog (Echinocereus engelmannii)
• Claret-cup Cactus (Echinocereus triglochidiatus)
• Green Hedgehog (Echinocereus viridiflorus)
• Rainbow Cactus (Echinocereus pectinatus)
• Pencil Cholla (Cylindropuntia arbuscula)
• Teddy-bear Cholla (Cylindropuntia bigelovii)
• Santa Rita Prickly-pear (Opuntia santa-rita)
• Arrastradillo (Opuntia stenopetala)
• Grizzly Bear Cactus (Opuntia polyacantha var. erinacea)
• Indian Fig (Opuntia ficus-indica)
• Christmas Cholla (Cylindropuntia leptocaulis)
• Diamond Cholla (Cylindropuntia ramosissima)
• Buckhorn Cholla (Cylindropuntia acanthocarpa)
• Staghorn Cholla (Cylindropuntia versicolor)
• Cane Cholla (Cylindropuntia imbricata)
• Cardón (Pachycereus pringlei)
• Sina (Stenocereus alamosensis)
• Barrel Cactus (Ferocactus cylindraceus)
• Coast Barrel Cactus (Ferocactus viridescens var. viridescens)
• Mexican Fence Post (Pachycereus marginatus)
• Senita (Pachycereus schottii)
• Organ Pipe (Stenocereus thurberi)
• Common Fishhook Cactus (Mammillaria tetrancistra)
Mammillaria albicans
Mammillaria blossfeldiana
Mammillaria guelzowiana
• Straw-spine Cactus (Thelocactus bicolor)
• Snowball Cactus (Mammilloydia candida)
• Arizona Beehive Cactus (Escobaria vivipara)
• Bishop’s Cap (Astrophytum myriostigma)
Cleistocactus spp.
• Easter Lilies (Echinopsis spp.)
• Torch Cactus (Echinopsis candicans)
• Desert Agave (Agave deserti)
• Mescal Ceniza (Agave colorata)
• Octopus Agave (Agave vilmoriniana)
• Mohave Yucca (Yucca schidigera)
• Our Lord’s Candle (Yucca whipplei)
• Banana Yucca (Yucca baccata)
• Joshua Tree (Yucca brevifolia)
• Sotols (Dasylirion spp.)
• Giant Hesperaloe (Hesperaloe funifera)
• Red Yucca (Hesperaloe parviflora)
• Manfredas (Manfreda spp.)
• Beargrasses (Nolina spp.)
• Slipper Plant (Pedilanthus macrocarpus)
Euphorbia xantii
• Globeberry (Ibervillea tenuisecta)

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As the weather warms, plant water needs will increase. Now is the time to adjust your watering schedule for the summer. Observe plants regularly for signs of water stress. Some signs to look for include:  wilting, curling leaves, yellowing or falling of older leaves, and dead stems or branches.

The amount of water and watering frequency depends on many factors. These include:  soil type, weather (temperature, humidity, rainfall, etc.), microclimates, cultural practices, plant size and species, and whether newly planted or established in the landscape (two years or more). Below are general guidelines to help you determine how much and how often to water your landscape and container plantings to keep them healthy when rainfall is lacking. View our Desert Gardening Guide on Watering Desert Trees and Shrubs for additional information.

Established native or desert-adapted trees and shrubs should be watered at least once to twice monthly. Water at least 3 feet deep for your trees and 2 feet deep for your shrubs. Always allow soil to dry out between each irrigation cycle.

Natural rainfall may be adequate for most well-established cacti and succulents. However, if rainfall is insufficient, water may be needed at least once to twice during the month of May. Water your cacti and succulents to a depth of at least 8-12 inches. Always allow soil to dry out between each irrigation cycle.

Established herbaceous perennials, groundcovers and vines should be watered every two to three weeks and at least 1 foot deep. Always allow soil to dry out between each irrigation cycle.

Wait a week after planting your cacti and succulents before watering to minimize the chance of rot. After the initial irrigation of your succulents, allow the soil to dry out and water every 10-14 days. Cacti need to be watered once more after initial watering during the month, but allow the soil to dry out between watering.

Newly planted native and desert-adapted trees and shrubs may need to be watered more frequently until established. It can take up to 3-5 years for trees and at least 1-2 years for shrubs to become established in the landscape.  After planting your trees and shrubs, they should be watered immediately and the moisture monitored for the next few days to keep the root ball from drying out. Schedule your irrigation cycle for trees and shrubs every 7-10 days during the month. Allow the soil to dry out between irrigations and always water deeply, 3 feet for trees and 2 feet for shrubs.

Newly planted native and desert-adapted herbaceous perennials, groundcovers and vines should also be watered immediately and for the next few days to keep the root ball from drying out. Schedule your irrigation cycle for herbaceous perennials, groundcovers and vines for at least once to twice weekly and to a depth of 1 foot. Allow soil to dry out between watering.

Agaves and other succulents (Aloe spp., Pachypodium lamerei, Beaucarnea recurvata, Pedilanthus macrocarpus, Euphorbia spp., Gasteria spp., Haworthia spp.) in containers should be watered at least once to twice this month. Cacti in containers should be watered at least once this month. However, cacti and succulents in small containers may need to be watered more often especially cacti and succulent seedlings.

Keep an eye on your warm-season annuals and herbaceous perennials in containers. Water them at least once to three times weekly.

Herbs may need to be watered every 3-5 days and vegetables need to be watered every 2-3 days. Water your herb and vegetable plants to at least a foot in depth.

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What to plant

Planting can still be done during the month of May. However, it is crucial that newly planted plants are monitored carefully. Follow the watering schedule for newly planted plants in the watering section above.

Plant warm-season cacti & succulents including: 
• Saguaro (Carnegiea gigantea)
• Prickly-pears (Opuntia spp.)
• Chollas (Cylindropuntia spp.)
• Barrel cacti (Ferocactus spp.)
• Hedgehogs (Echinocereus spp.)
• Pincushions (Mammillaria spp.)
• Easter Lilies (Echinopsis spp.),
• Paper-spine Cholla (Tephrocactus articulatus var. papyracanthus)
• Agaves (Agave spp.)
• Aloes (Aloe spp.)
• Candelilla (Euphorbia antisyphilitica)
• Desert Spoon (Dasylirion wheeleri)

• Giant Hesperaloe (Hesperaloe funifera)
• Slipper Plant (Pedilanthus macrocarpus)
• Elephant Food (Portulacaria afra)
• Burseras, Elephant Trees (Bursera spp.)
• Madagascar-palm (Pachypodium lamerei)
• Madagascar-ocotillo (Alluaudia procera)
Dyckia spp.
• Carrion Flowers (Stapelia spp.)
• Texas-tuberose (Manfreda maculosa)
• Limberbushes (Jatropha spp.)
• Red-yucca (Hesperaloe parviflora)


Most Yuccas (Yucca spp.) can be planted with the exception of Joshua Trees (Yucca brevifolia).

When transplanting cacti and succulents, mark either the south or west side and plant facing the orientation you marked to avoid the burning of tender tissues. Most nurseries will mark the side of the container to help you determine proper planting orientation. However, if the original orientation is not known, newly planted cacti and succulents need to be covered with shade cloth if the plant surface appears to yellow or pale suddenly. Use a shade cloth rated between 30-60% as anything higher will block most of the sunlight and will not be suitable for your cacti and succulents. You may need to keep the shade cloth on the plant for the duration of the summer.

Plant native and desert-adapted trees including: 
• Ironwood (Olneya tesota)
• Blue Palo Verde (Parkinsonia florida)
• Little-leaf Palo Verde (Parkinsonia microphylla)
• Mesquites (Prosopis spp.)
• Golden Leadball Tree (Leucaena retusa)
• Desert-willow (Chilopsis linearis)
• Palo Blanco (Mariosousa willardiana syn. Acacia willardiana)
• Catclaw Acacia (Senegalia greggii syn. Acacia greggii)
• Canyon Hackberry (Celtis laevigata var. reticulata syn. Celtis reticulata)
• Texas-ebony (Ebenopsis ebano)
• Twisted Acacia (Vachellia bravoensis syn. Acacia schaffneri)
• Feather Tree (Lysiloma watsonii)
• Anacacho Orchid-tree (Bauhinia lunarioides)
• Vitex (Vitex agnus-castus)
• Baby Bonnets (Coursetia glandulosa)
Plant warm-season shrubs including: 
• Yellow Bells (Tecoma spp.)
• Texas-sages (Leucophyllum spp.)
• Creosote (Larrea tridentata)
• Superstition Mallow (Abutilon palmeri)
• San Marcos Hibiscus (Gossypium harknessii)
• Desert Cotton (Gossypium thurberi)
• Guayacán (Guaiacum coulteri)
• Sennas (Senna spp.)
• Velvet-pod Mimosa (Mimosa dysocarpa)
• Ocotillo (Fouquieria splendens)
• Fire Bush (Hamelia patens)
• Ruellia (Ruellia peninsularis)
• Lantana (Lantana camara)
• Mexican Bush Sage (Salvia leucantha)
• Silver Nightshade (Solanum hindsianum)
• Little-leaf Cordia (Cordia parvifolia)
• Showy Mendora (Menodora longiflora)
• Sky Flower (Duranta erecta)
• Bird of Paradise species (Caesalpinia spp.)
Plant warm-season herbaceous perennials and groundcovers including:
• Sacred Datura (Datura wrightii)
• Desert Four O’Clock (Mirabilis multiflora)
• Arizona Foldwing (Dicliptera resupinata)
• Buffalo Gourd (Cucurbita foetidissima)
• Mealy-cup Sage (Salvia farinacea)
• Yerba Mansa (Anemopsis californica)
• Rose-mallow (Hibiscus coulteri)
• Wine Cups (Callirhoe involucrata)
• Hummingbird Trumpet (Epilobium canum ssp. latifolium)
• Chocolate Flower (Berlandiera lyrata)
• Desert Senna (Senna covesii)
• Trailing Lantana (Lantana montevidensis)
• White Plumbago (Plumbago scandens)
• Mist Flower (Conoclinium dissectum)
• Rain-lilies (Zephyranthes spp.)
Many vines can also be planted at this time including:
• Yuca (Merremia aurea)
• Queen’s Wreath (Antigonon leptopus)
• Yellow Orchid-vine (Callaeum macropterum)
• Passionflowers (Passiflora spp.)
• Arizona Canyon Grape (Vitis arizonica)
• Old Man’s Beard (Clematis drummondii)




When planting native and desert-adapted plants, it is usually unnecessary to back-fill with soil amendments and vitamins or to add rooting hormones. However, a slow-release fertilizer high in nitrogen and phosphorous can be added to the backfill, if needed. Take a look at our Desert Gardening Guide on How to Plant Desert-Adapted Trees and Shrubs.

Many cacti can be started from seed at this time.  Seed can be soaked overnight in water to help start the germination process. Place seed in a well-draining soil mix (½ quality potting soil and ½ perlite or pumice) and lightly cover with potting mix or gently press seed into the soil. Keep soil moist until germination occurs. See our Desert Gardening Guide on Growing Cacti from Seed.

Sow seed of warm-season herbaceous perennials including:
• Mexican Hat (Ratibida columnifera)
• Red Sage (Salvia coccinea)
• Desert Senna (Senna covesii)
• Sacred Datura (Datura wrightii)
• Mealy-cup Sage (Salvia farinacea)
Vegetables to transplant include:  
• Jerusalem artichoke
• sweet potato
• watermelon
• tomatillo
• jicama
• eggplant and pepper (by mid-month)
Vegetable seeds to sow include:   
• Black-eyed peas (early part of May)
• cantaloupe
• okra
• tepary beans
• muskmelon
• tomatillo
• yardlong bean
• pumpkin
• summer and winter squash
• watermelon
Try the variety of melons from Native Seeds/SEARCH.
Herbs to transplant include:  
• basil
• Mexican-oregano (Lippia graveolens)
• Mexican-tarragon (Tagetes lucida)
• Cuban-oregano
Herbs seeds to sow include: 
• amaranth




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Pruning should be done to maintain plant health (remove dead, damaged or diseased portions, cross branching, etc.), to highlight the “natural” shape of the plant, to train a young plant, and to eliminate hazards. Excessive or heavy pruning causes significant stress to trees and shrubs. The best practices are to prune the least amount necessary and prune for legitimate reasons. How much to prune depends on the size, species, age, as well as your intentions. Two good principles to remember--a tree or shrub can recover from several small pruning wounds faster than from a single large wound and never remove more than 25% of the canopy in a year. For more information register for a Garden class offered on pruning that will teach you the proper pruning techniques for trees and shrubs or visit for information on proper pruning of young and mature trees.

If necessary, native and desert-adapted spring-flowering shrubs can be pruned after flowering has diminished. However, prune before the upcoming hot, summer months. For more information on pruning shrubs go to the University of Arizona Cooperative Extension at:

Lightly prune your Mesquites (Prosopis spp.) and Palo Verdes (Parkinsonia spp.) to remove dead and crossing branches.

Pruning newly planted trees and shrubs is not recommended and in fact, can be detrimental.  However, at planting time prune broken or torn and diseased branches. Save other pruning activities for the second or third year. For more information on developing a healthy tree visit

Prune Prickly-pears (Opuntia spp.) or Chollas (Cylindropuntia) after flowering.   If pruning your prickly-pears or chollas to maintain size, for propagation or to remove a damaged or diseased stem, prune at the joint or segment.  Use a sharp, clean pruning tool and spray tool periodically with a 70% alcohol solution to prevent infection. If the pruned stem is to be used for propagation, allow the cutting to dry out for a week before planting. Check out our Desert Gardening Guide on Rooting a Cactus Cutting for more information.

Continue to remove spent stalks of aloes, agaves and other succulents.

Spring-blooming perennials such as Penstemons (Penstemon spp.), Brittlebush (Encelia farinosa), Globemallow (Sphaeralcea ambigua), Fleabane (Erigeron divergens), and Golden Columbine (Aquilegia chrysantha) should be producing seed. Allow them to produce seed before pruning spent flowering stems. The seed is a valuable food source for many animals.

Deadhead herbaceous perennials to encourage continued flowering including Desert Marigold (Baileya multiradiata), Chocolate Flower (Berlandiera lyrata), Red Sage (Salvia coccinea), Mealy-cup Sage (Salvia farinacea), Gaura (Gaura lindheimeri), Tickseeds (Coreopsis spp.), Angelita-daisy (Tetraneuris acaulis), and Gaillardia (Gaillardia pulchella).

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Most native and desert-adapted plants in the landscape do not generally require fertilizer as they are adapted to our soil conditions. In most cases, fertilizers are generally applied to prevent deficiencies. If fertilizers are needed, one application for the year is usually sufficient. If you did not fertilize in March or in April, go ahead and fertilize your landscape plants if necessary.  However, it is recommended to fertilize your landscape plants the early part of May. For more information on fertilizing and plant deficiencies go to the University of Arizona Cooperative Extension Publications: and /sites/dbg.dd/files/nutrient_deficiencies.az1106.pdf0_s.pdf

Periodically fertilizing may be needed for plants in containers as nutrients in the soil will have diminished over time. Always follow directions on the label.

Continue to fertilize your warm-season annuals and herbaceous and woody perennials in containers if necessary. 

Cacti and warm-season succulents in containers should be fertilized at least once during the month. Do not fertilize any winter-growing succulents such as Live Forever (Dudleya saxosa ssp. collomiae), Succulent Geraniums (Pelargonium spp.), Iceplants (Malephora spp., Drosanthemum spp., Cephalophyllum spp.), Living Stones (Lithops spp.) and crassulaceous plants (Kalanchoe spp., Cotyledon spp., Echeveria spp.) as they are now undergoing their summer dormant period.

Continue to fertilize your vegetable and herb garden as needed.

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A noticeable, fine web may be present on your Palo Verde trees (Parkinsonia spp.) and even from time to time on the Whitethorn Acacia (Vachellia constricta syn. Acacia constricta).  This “webbing” is produced by the Palo Verde webworms often called Palo Verde webbers. The webworm is a small caterpillar that feeds on the leaves and occasionally the bark of the small stems.  The Palo Verde tree and Whitethorn Acacia are resilient to webworm infestations so control methods are unnecessary. The caterpillars and adult moths are an important food source for many lizards and birds.

If you notice a tattered appearance on your landscape plants such as Evening Primroses (Oenothera spp.), Sacred Datura (Datura wrightii) and Gaura (Gaura lindheimeri) it may be the flea beetle in action. A different species of flea beetle may also harm your vegetables including tomatoes and eggplants. The flea beetle larvae and adults can be destructive and they can be difficult to control. To find out more information on flea beetles go to the following link:

Agave snout weevils become active during the warm months and infestation may not be apparent until it is too late. For detailed information on the life cycle, symptoms, prevention and treatment go to our Agave Snout Weevil Desert Gardening Guide.

While sitting underneath your desert trees, you may notice a light “rain” falling. This is the smoke tree sharpshooter insect expelling sap as it draws from a variety of plants including Palo Verdes (Parkinsonia spp.), Beebrush (Aloysia gratissima), Bird of Paradise species (Caesalpinia spp.) and Hackberries (Celtis spp.). These sharpshooter insects have gone virtually unnoticed until they threatened oleanders, shrubs widely used in low-desert landscapes for screening hedges. They gained notoriety because they are able to transmit a deadly bacterial disease called oleander leaf scorch. Our native plants do not appear to be adversely affected by the smoke tree sharpshooter so no control is necessary.  To find out more about oleander leaf scorch check out the University of Arizona Extension Plant Pathology at

As the weather warms, whiteflies may be present on your landscape, vegetable and herb plants. These tiny, white insects have sucking mouthparts that cause leaves to yellow, wilt and drop prematurely. The immature nymph stage does more harm to the plant than the adult. Whiteflies can be difficult to control. Allow natural predators such as spiders, ladybugs, lacewings and even hummingbirds to control the population. Yellow sticky traps can also be used to control the adult population.

Noticeable leaf damage may be seen on the Texas Mountain-laurel (Calia secundiflora syn. Sophora secundiflora) during the warm months. The damage is caused by the sophora pyralid caterpillars feeding on the tender new growth. These ravenous caterpillars are approximately an inch long with orange bodies and interesting black spots with white hairs. To find out more information about the Sophora pyralid moths go to our Desert Gardening Guide.

Psyllids can still be active during the month of May, but activity will decrease as the temperatures climb.  Psyllids are sap feeders and many are plant specific or feed on a closely related group of plants. High populations of psyllids can cause distortion and die back of new growth, and in some cases defoliation. To keep populations under control do not overwater or over fertilize your plants as this causes excessive growth. Yellow sticky traps can also be used to control the adult population.

Cochineal scale, the cottony, white substance on your Prickly-pears (Opuntia spp.) and Chollas (Cylindropunita spp.) may be active now. Remove by using a fast stream of water or spray insecticidal soap.

Fine webbing between leaves or stippling on leaves may indicate the presence of spider mites. These plant mites cause damage by sucking contents from the leaves and are difficult to detect due to their small size. Plants that are water stressed may become susceptible to infestation. Dusty conditions can also lead to spider mite outbreaks. Make sure your plants are well-watered and wash off accumulated dust on plants to manage spider mite problems. You can also remove by using a fast spray of water or by spraying insecticidal soap to control populations. There are many biological controls that feed on spider mites including lacewings, predatory mites, lady bugs and big-eyed bugs. Using insecticides is not recommended as insecticides do not help manage the population, but can actually cause the population to intensify because insecticides used will often kill their natural enemies. Some insecticides can even accelerate mite reproduction.

If you notice a rank odor and black ooze dripping down the saguaro stem(s), the plant may have developed an infection as a result of an injury or frost damage. The infection is caused by the Erwinia bacteria, a common bacterium found in the environment.  For more information on saguaros and how to care for them, check out our Desert Gardening Guide Planting and Caring for a Saguaro.

For more information on diseases or problems of landscape plants go to the University of Arizona Cooperative Extension publication /sites/dbg.dd/files/pldiseases_urban-1124.pdf or the University of California UC IPM Online at

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