Common diseases and insect pests that affect Utah cucurbit production.

1. Nick Volesky
Pests of
Pumpkins
and Squashes
in Utah

2. Overview of Pumpkin
& Squash Diseases
Common Name Casual Agent
Virus
Beet Curly Top Virus curtovirus
Cucumber Mosaic Virus cucumovirus
Watermelon Mosaic Virus potyvirus
Zucchini Yellow Mosaic Virus potyvirus
Fungus
Gummy Stem Blight (Black Rot) Didymella bryoniae
Pythium Root & Fruit Rot Pythium sp.
Fusarium Wilt Fusarium solani f. sp. Cucurbitae
Damping-Off *fungal complex
Powdery Mildew Podosphaera xanthii
Verticillium Wilt Verticillium dahliae
Phytophthora Root Rot Phytophthora sp.
White Mold Sclerotinia sclerotiorum

3. Damping-Off
• various fungal species (Pythium,
Phytophthora, etc.)
• widespread in Utah transplant
production
• kills vascular tissue within seedling
stem

4. • water when needed and remove
diseased plants immediately
• sterilize pots in 10% bleach for one
hour; rinse
• clean and disinfect greenhouse
benches with bleach
• use a barrier between pots and dirt
floor
Damping-Off
Management

5. Powdery Mildew
• Podosphaera xanthii and
Erysiphe cichoracearum
• widespread in Utah
• white, “powdery” fungal growth
(mycelium) occurs primarily on foliage
• infection occurs via windborne spores
season long
• as leaves become colonized, they may
turn yellow and wilt
• ideal conditions are 65-85˚ with high
humidity in canopy (no rainfall)

6. Powdery Mildew Management
• remove early infected leaves as they
become encountered
• some resistant cultivars are available
• provide adequate plant spacing
• remove old debris and volunteers
• fungicides: copper, sulfure + pyrethrins,
chlorathalonil, myclobutanil, Bacillus
subtilis, mineral oils, and plant-based oil
products

7. • curtovirus
• rare on Utah pumpkins and squashes
• vectored by the beet leafhopper
(Circulifer tenellus)
• concern during spring and summer
when beet leafhoppers are moving
from weeds to vegetable crops
• plants are infected randomly
• small, twisted, curled leaves with
purple veins
• thickened, stiff, and crisp leaves
• prematurely ripened fruit
Beet Curly Top Virus

8. Cucumber Mosaic Virus
• cucumovirus
• rare on Utah pumpkins and squashes
• spread by aphid feeding and human
handling
• plant stunting
• mosaic pattern of yellow-light green
patches
• ring spots, patterns on fruits

9. • potyvirus
• common on Utah pumpkins and squashes
• vectored by aphid feeding
• plant stunting
• leaf malformation (raised blister-like areas)
• warts and discoloration on fruits
Watermelon Mosaic Virus

10. • potyvirus
• rare on Utah pumpkins and squashes
• spread by aphid feeding and human
handling
• stunted plant growth
• warts, distortion and discoloration on fruits
Zucchini Yellow Mosaic Virus

11. • sanitation – disinfect tools when
working between crops
• remove virus-infected plants
• remove nearby weeds that might
serve as an alternate host
• control insect populations that vector
the viruses
• no chemical control options for
viruses
Virus Management

12. • Didymella bryoniae
• occasional on Utah pumpkins and
squashes
• affects foliage, stems, and fruit
• stems ooze “gum”
• necrotic concentric rings on fruit
• seed- and soilborne
• optimal conditions 65°-75° F and long
periods of moisture
Gummy Stem Blight (Black
Rot)

13. • Pythium spp.
• occasional on Utah pumpkins and
squashes
• white mycelium and resemble “cotton”
• infection occurs through wounds or where
fruit touches the wet soil
• pathogen overwinters on crop debris,
weeds, and as resting structures in the soil
Pythium Fruit & Root Rot

14. • Phytophthora spp.
• rare on Utah pumpkins and squashes
• pathogen moves through splashed
and surface water on infected soil
• fruits may be infected
• plant crown and roots are infected
Phytophthora Root Rot

15. • Sclerotinia sclerotiorum
• rare on Utah pumpkins and squashes
• Infected fruit and stems first appear water-
soaked
• fluffy, white, cotton-like fungal growth
• small, hard, black fungal structures, (sclerotia)
develop in mold
• white mold often infects fruit through the
blossom end. They become rotted and
watery. Sclerotia may be present inside the
rotted fruit.
• rot may occur in the field or post-harvest
White Mold

16. • source certified disease-free seed or
treat seeds
• rotate cucurbit crops for 2-3 years to
avoid outbreaks in the field
• implement drip irrigation and plastic
mulch
• staking/mulching can prevent fruit
contact with the soil
• fungicides: mefenoxam (root rot
only), chlorothalonil, mineral oils (read
labels)
Rot & Mold Management

17. • Fusarium solani f. sp. Cucurbitae
• common on Utah pumpkins and
squashes
• seed- and soilborne
• marginal yellowing progressing to a
general yellowing of older leaves
• stems near the crown, linear/necrotic
lesion may develop
Fusarium Wilt

18. • Verticillium dahliae
• widespread on Utah pumpkins and
squashes
• wilting and yellowing of crown leaves
• light brown vascular discoloration in roots
is sometimes seen in cross section
Verticillium Wilt

19. Wilt Management
• plant resistant varieties when they’re
available (grafting)
• source disease-free certified seed
• clean equipment and shoes from the
attached soil
• plant on raised beds for better water
drainage
• grow mustards as cover crop, they have
bio fumigant properties
• no chemical controls for verticillium and
fusarium wilt

20. Overview of Pumpkin
& Squash Insect Pests
Family Common Name Scientific Name
Aphididae
Green Peach Aphid Myzus persicae
Melon Aphid Aphis gossypii
Potato Aphid Macrosiphum euphorbiae
Chrysomelidae
Western Spotted Cucumber
Beetle
Diabrotica undecipunctata undecipunctata
Western Striped Cucumber
Beetle
Acalymma trivittatum
Tetranychidae Twospotted Spider Mite Tetranychus urticae
Coreidae Squash Bug Anasa tristis
Acridae Grasshoppers Suborder: Caelifera
Armadillidiidae Pillsbug Armadillidium vulgare
Thripidae
Western Flower Thrips Frankliniella occidentalis
Onion Thrips Thrips tabaci

21. Aphids
• several species
• small, pear-shaped, soft bodies
• reproduce asexually
• multiple generations a season
• overwinter as eggs on woody hosts
• adults and nymphs feed with piercing-
sucking mouthparts causing stippling, leaf
curling, etc.
• active mid-April though the end of the
growing season
• vector viral diseases

22. Aphid Management
• manage nitrogen levels
• encourage natural enemies
• keep crop area weed-free
• insecticides: malathion, permethrin,
pyrethrins, zeta-cypermethrin, insecticidal
soap, plant-based oils, pyrethrins + sulfur

23. Cucumber Beetles
• adults are yellow (black spots or stripes
depending on species)
• larvae are worm like with brown heads
• overwinter as adults
• adults become active at temperatures
above 50˚ F in the spring
• feeding damage is most critical from the
cotyledon through early true-leaf stages

24. Cucumber Beetle
Management
• keep production area weed free
• use floating row covers
• use plastic or organic mulches and drip
irrigation
• destroy crop residues after harvest
• lure beetles away with traps/lure
• insecticides: carbaryl, malathion,
cyfluthrin, permethrins, zeta-
cypermethrin, pyrethrins + sulfur

25. Spider Mites
• arachnid
• best observed with a hand lens
• piercing-sucking mouthparts (leads to
stippling)
• webbing
• generalized bronzing/reddish
discoloration develops as populations
increase
• active during hot and dry conditions
• overwinter as adults in ground covers

26. Spider Mite Management
• keep plants healthy and free of drought
stress
• encourage natural enemies such as
predatory mites
• spider mites develop high resistance to
pesticides
• insecticides: pyrethrins + canola oil,
pyrethrins + sulfur, plant based oils,
insecticidal soap

27. Squash Bugs
• adults are flat and brown/grey with
orange/brown bands
• eggs are shiny bronze
• nymphs are bright green become more
grey/brown
• 1 generation/year (northern/central Utah)
2nd partial generation/year (Washington
Co.)
• Overwinter as adults in protected sites
around building and under plant debris
• early monitoring for eggs is critical

28. Squash Bug Management
https://extension.usu.edu/pests/files/pubs
/Squash-Bug-Infographics.pdf

29. Thrips
• very small
• elongated yellow-brown bodies
• two pairs of fringed (hairy) wings
• feed with a punch-and-such behavior
• cause flecking wounds and silvery scars
on foliage
• populations are favored by hot, arid
conditions

30. Thrips Management
• plow under plant debris after harvest
and remove volunteer host plants
• use overhead sprinkler irrigation to wash
thrips away from plants
• remove weeds near production site
• thrips develop rapid resistance to several
classes of insecticides, so they’re
generally not recommended

31. Contact
Nick Volesky (Vegetable IPM Associate)
nick.volesky@usu.edu
(435) 797-0319
USU Extension – Utah Pests
@utah_pests