Summer Insect Pests, Plant Diseases, and Abiotic Challenges

Earwigs

Identification: Earwigs (Forficula auricularia) are elongated insects, typically measuring about 1 to 3 centimeters in length. They have long, slender bodies with pincer-like appendages at the rear, called cerci. Common earwigs are usually dark brown or black, but their appearance can vary. These pincers are used for defense and mating, but earwigs are not harmful to humans.

Management:

• Cultural Practices: Implement good cultural practices to minimize earwig populations. This includes removing debris, mulch, and excess vegetation around the crop area where earwigs may hide. Tilling or turning the soil can help expose and disrupt these hiding places.
• Habitat Modification: Remove or reduce potential hiding spots, such as piles of garden debris, rocks, and boards. Regularly clean up the garden area to reduce shelter options for earwigs.
• Traps: Place container bait traps near the base of affected plants in the evening. Earwigs will seek shelter in these traps during the day, making it easier to collect and remove them manually.
• Chemical Control: If earwig populations become excessively high and begin causing significant damage, insecticides may be used as a last resort. Use only products labeled for earwig control, and always follow the manufacturer’s instructions and safety guidelines. Be mindful of the potential impacts on beneficial insects and the environment.

Squash Bugs

Squash bugs are a major pest of cucurbit crops such as winter squash, summer squash, melons, cucumbers, and cantaloupe. These insects can cause significant damage, including plant death. Using piercing-sucking mouthparts, they extract large quantities of plant sap. Fortunately, in Utah, squash bugs do not transmit plant diseases.

Identification: Adult squash bugs are approximately 5/8 inch long and have wings that lie flat over their backs. When disturbed, they emit a foul odor, which leads to their occasional misidentification as stink bugs; however, true stink bugs belong to a different insect family. Squash bugs develop through five nymphal stages, ranging in color from reddish to green-gray. Their eggs are shiny bronze and are typically found on the undersides of leaves.

Biology: Squash bugs overwinter as adults in protected areas such as plant debris, compost piles, and near building foundations. They emerge in spring—typically in April in southern Utah and May in northern Utah—and fly to host plants to feed, mate, and lay eggs. Each female can lay up to 250 clusters of 4 to 40 eggs on the undersides of leaves. The eggs hatch into nymphs, which take 4 to 6 weeks to mature into adults. The summer generation appears in late July in northern Utah and 3 to 4 weeks earlier in southern Utah. These adults feed on cucurbits to build fat reserves for overwintering.

Damage:

• Scarring and sunken, desiccated areas on fruits
• Daytime wilting of foliage due to xylem and phloem damage (with recovery at night)
• Complete plant decline in severe infestations

Management:

One of the most effective ways to manage squash bugs is through regular monitoring and physical removal of eggs and insects.

• Inspect plant debris and perennial plants in the spring for overwintered adults.
• Check the undersides of leaves regularly for eggs.
• Remove or kill eggs using duct tape, petroleum jelly, or by cutting out the affected section of the leaf.
• Hand-remove adults and nymphs and drown them in soapy water.
• Pull out plants immediately after harvest to eliminate overwintering sites.
• Rotate crops with non-cucurbits to reduce populations.
• Choose cucurbit varieties with known resistance, such as butternut and royal acorn squash.

Adult squash bugs have some tolerance to insecticides due to their body structure and tendency to hide deep in the plant canopy. For best results, apply insecticides shortly after egg hatch to target the more vulnerable nymphs. Ensure thorough spray coverage of the entire plant canopy, including leaf undersides, vines, and fruits. Avoid spraying during bloom periods to protect pollinators.

Powdery Mildew in Vegetables

Powdery mildew is widespread in Utah and affects a variety of vegetable, fruit, and landscape plants. Multiple species of powdery mildew fungi exist, with each typically targeting a specific host or closely related plant families. These fungi are obligate parasites, meaning they require a living host to grow.

Powdery Mildew Species	Host Crops
Erysiphe cruciferarum	Broccoli, cabbage, cauliflower, kale, and Brussels sprouts
Erysiphe polygoni	Chard, beet, and beans
Erysiphe pisi	Pea
Erysiphe heraclei	Carrot and celery
Golovinomyces cichoracearum	Cucumber, melon, summer squash, and winter squash
Podosphaera xanthii	Cucumber, melon, summer squash, and winter squash
Leveillula taurica	Onion, pepper, and tomato

Biology: Late in the growing season, powdery mildew fungi reproduce sexually, forming chasmothecia on foliage. These structures contain overwintering spores that are resistant to cold and drought. In spring, the spores are released and initiate primary infections in suitable hosts.

Powdery mildew spores can germinate without free moisture. Once on a host, they form hyphae that colonize the leaf surface, using haustoria to penetrate host cells and extract nutrients. Within 7 to 10 days, white mycelium and spores (conidia) become visible. The rapid production of conidia leads to multiple secondary infections throughout the season. Warm, dry conditions (75–85°F), combined with high evening humidity, can result in rapid disease spread and potential epidemics—especially in older foliage and densely planted crops.

Monitoring:

Early detection is essential.

• Commercial growers should inspect 5–10 random locations in the field weekly.
• Home gardeners should check all plants regularly.
  Focus on the tops and undersides of older, mature leaves, particularly in areas that are densely planted, shaded, weedy, or growing vigorously.

Management:

• Plant Resistant Varieties: Choose vegetable varieties labeled with resistance to powdery mildew. Be aware that Podosphaera xanthii has multiple races, and resistant varieties may not protect against all of them—many of which remain unidentified in Utah.
• Remove Infected Plant Material: After harvest, remove or plow under infected debris, as powdery mildew can overwinter in plant material. Destroy all affected leaves, branches, vines, and fruit. Do not compost them, as composting temperatures are insufficient to eliminate the pathogen.
• Increase Plant Spacing: Adequate spacing improves air circulation and reduces canopy humidity, which helps prevent infection.
• Irrigate in the Morning: Watering early allows soil and foliage to dry before nightfall, reducing humidity. Whenever possible, use drip irrigation to limit moisture on leaves.
• Fungicide: A range of organic and synthetic fungicides is available for both commercial growers and home gardeners. Begin treatment at the first sign of disease. Reapply every 7–10 days, or as directed on the product label.
  • Caution: Avoid Phytotoxicity
    Some products or combinations can cause plant injury:

• • • Avoid applying oils when temperatures exceed 85°F.
    • Avoid applying sulfur when temperatures exceed 80°F.
    • Do not apply oil and sulfur within two weeks of each other.

Vegetable Wilting Caused by Soilborne Pathogens

Fusarium wilt and Verticillium wilt are soilborne plant diseases that attack vascular tissue, causing similar wilting symptoms in affected plants. These diseases are difficult to manage because the pathogens can persist in soil for many years. Once a plant becomes infected, there is no effective treatment or cure, making preventive and cultural management strategies essential.

Both pathogens have a broad host range among vegetable crops in Utah. Fusarium oxysporum is typically categorized into formae speciales (f. sp.) based on the specific hosts it infects. Each forma specialis can be further divided into races (e.g., 1, 2, 3) depending on the resistance genes present in the host cultivar. Verticillium dahliae and V. albo-atrum are the two major species that cause Verticillium wilt. Hosts for each pathogen are listed below:

Pathogen		Host
Fusarium oxysporum f. sp. apii		Celery
Fusarium oxysporum f. sp. asparagi		Asparagus
Fusarium oxysporum f. sp. batatas		Sweet potato
Fusarium oxysporum f. sp. betae		Beet
Fusarium oxysporum f. sp. cepae		Garlic, onion
Fusarium oxysporum f. sp. ciceris		Chickpea
Fusarium oxysporum f. sp. conglutinans		Broccoli, Brussels sprouts, cabbage, cauliflower, kale
Fusarium oxysporum f. sp. cucumerinum		Cucumber
Fusarium oxysporum f. sp. cucurbitae		Summer and winter squash
Fusarium oxysporum f. sp. lactucae		Lettuce
Fusarium oxysporum f. sp. lycopersici		Eggplant, pepper, tomato
Fusarium oxysporum f. sp. melonis		Cantaloupe
Fusarium oxysporum f. sp. niveum		Watermelon
Fusarium oxysporum f. sp. phaseoli		Bean
Fusarium oxysporum f. sp. pisi		Pea
Fusarium oxysporum f. sp. spinaciae		Spinach
Fusarium oxysporum f. sp. tracheiphilum		Black-eyed pea
Pathogen	Host
Verticillium dahliae	Artichoke, broccoli, Brussels sprouts, cabbage, cauliflower, cantaloupe, cucumber, kale, lettuce, squash, watermelon
Verticillium albo-atrum	Beet, Brussels sprouts, cabbage, cauliflower, chickpea, kale, potato, squash, watermelon

Symptoms and Diagnosis

Fusarium wilt symptoms may take several weeks to appear, allowing young plants to be unknowingly infected. Wilting may occur on one side of the plant. Younger plants may temporarily recover in cool evening temperatures, while older leaves become chlorotic and eventually die. As temperatures rise, permanent wilting and plant death follow, often accompanied by brown discoloration in the vascular tissue.

Verticillium wilt symptoms typically begin on lower foliage, which becomes chlorotic and necrotic. In tomatoes, a V-shaped lesion forms along leaf margins. In potatoes, symptoms begin on the lower leaves. Eggplant leaves may droop, turn yellow, and roll inward. Photosynthesis is reduced, lowering fruit quality. Severe infections lead to full plant collapse and vascular discoloration.

To diagnose wilt, remove a recently wilted or dead plant, cut a cross-section of the lower stem, and check for brown vascular discoloration. This indicates wilt but cannot distinguish between Fusarium and Verticillium. Suspected samples should be submitted to the Utah Plant Pest Diagnostic Laboratory for confirmation.

Management Strategies

Because infected plants cannot be treated, preventing introduction and improving soil health are critical.

Preventing Introduction:

• Crop Rotation: Rotate crops to reduce buildup of soilborne fungi.
• Disease-Free Seed: Use certified disease-free seeds and tubers. Contaminated materials can occasionally harbor Fusarium or Verticillium.
• Sanitation in Greenhouses: Clean trays, pots, and tools with a 10–15% bleach solution or quaternary ammonium compounds. Rinse well to prevent residue phytotoxicity. Dispose of infected seedlings and soil mix.
• Clean Equipment: Remove soil from shoes, tools, and machinery before moving between fields.

Where Disease Is Present:

• Resistant Cultivars: Select varieties bred for resistance. Resistance is often race-specific (e.g., tomato, cantaloupe, pea).
• Remove Plant Residue: Remove and destroy infected plant material after the season to reduce overwintering fungi.
• Soil Solarization: In gardens and small plots, solarize soil during the hottest months (see UC ANR’s solarization guidelines).
• Soil Fumigation: In commercial fields, fumigation with metam sodium or chloropicrin may reduce microsclerotia but can harm soil health and may not be economically viable in Utah.
• Biofumigation: Use mustard-family cover crops rich in glucosinolates for potential disease suppression (see UVM’s biofumigation factsheet).
• Grafted Plants: Grafted vegetables (e.g., tomatoes) combine resistant rootstocks (like Estamino or Maxifort) with desirable fruiting varieties, improving plant survival.

Poor Root Development in Tomato Plants

In recent years, diagnostic sample submissions and field scouting reports have revealed tomato plants exhibiting poor root development. This condition can result from several factors, one of the most common being plants becoming rootbound within growing cells before transplanting. In such cases, adventitious roots may begin to develop higher up on the stem in an attempt to compensate.

Other contributing factors include improper planting depth, inconsistent irrigation, and soil type. When plants appear wilted or show signs of dieback, it is important to pull and inspect the roots. Rootbound plants often send out only a few roots into the surrounding soil, and if root rot pathogens are present, these roots can quickly decay—leaving the plant unable to take up sufficient water and nutrients.

Aboveground symptoms of root issues can resemble those caused by other stressors or diseases. For instance, some tomato plants may curl their leaves upward to reduce moisture loss during heat stress.

Sun Damage on Solanaceous Crops

Sunscald (sunburn) can occur on various fruiting crops when intense sunlight damages the fruit’s surface. Both green and fully ripened fruit are susceptible, especially when plants suddenly lose foliage that would otherwise provide shade.

Identification: In tomatoes, sunscald appears as white or light-colored, blister-like spots on the fruit. Over time, these areas may dry out, become sunken or flattened, and develop a papery texture. The injury can also create an entry point for rot-causing fungi or bacteria.

Prevention:

• Avoid heavy pruning during mid-to-late summer, as this can expose fruit to direct sunlight.
• Maintain proper water and nutrient management to support healthy leaf growth and canopy coverage.
• Minimize damage to foliage during harvest or field work—take care not to remove excessive amounts of leaves, vines, or branches.
• Use shade cloth (30% recommended) to reduce sun exposure and lower plant temperatures if needed.

Herbicide Damage on Broadleaf Vegetables

Tomatoes and other broadleaf vegetable crops are highly susceptible to herbicide injury, particularly during the heat of summer.

Herbicide damage can occur when broadleaf-targeting herbicides come into contact with vegetable plants either directly or indirectly—via spray drift, vaporization, or residual contamination in soil, mulch, or compost materials.

Symptoms:

• Small, misshapen leaves that are thick and tightly curled
• Stunted growth
• Dieback in cases of severe exposure

Plants may recover from minor herbicide injury, though yields are often reduced. Some herbicides can volatilize at high temperatures, allowing vapors to drift long distances. Others may drift as spray particles during windy conditions.

Prevention:

• Always follow label directions regarding application temperature, wind speed, nozzle size, and spray pressure.
• Use hooded sprayers, increase droplet size, and consider drift-reducing additives.
• Thoroughly clean sprayers after use.
• Avoid spraying when wind is blowing toward sensitive crops.

Tomato plants exposed to low levels of herbicide may recover over time. However, if damage is traced back to contaminated mulch or compost, discontinue its use immediately and remove the material to prevent further injury.