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Vegetables
Volume 65 Number 9 Date 06/25/2020 SQUASH VINE BORER - The summer flight has started. The emergence of moths signals that vegetable growers should begin checking vine crops for the flat, brown eggs deposited at the base of stems. Control is required immediately after the eggs are found to prevent the larvae from boring into the vines. Gardeners may remove the eggs by scraping with a fingernail. Covering plants with row covers or netting to prevent egg deposition and placing yellow pheromone-baited sticky traps around plantings may also help to reduce problems. A conventional insecticide or kaolin clay applied to the plant bases as a weekly spray during the three- or four-week egg laying period can provide protection if the sprays thoroughly cover the plant stems and are applied repeatedly to assure good control. POTATO LEAFHOPPER - Nymphs are appearing in vegetable crops and early July heat could cause an abrupt population increase. A threshold of one nymph per 10 leaves or one adult per sweep indicates control is justified for snap beans. The threshold for potatoes is 2.5 nymphs per 25 leaves or 0.5-1.0 adult per sweep. RED TURNIP BEETLE - This red and black beetle has been observed in central Wisconsin alfalfa. Red turnip beetle is a sporadic pest in the Central Sands area of the state, feeding on plants in the mustard family. Hosts include broccoli, cabbage, kohlrabi, radish and turnip, but hoary alyssum and yellow rocket are thought to be the primary food plants. Small seedlings and transplants are the most susceptible to red turnip beetle feeding, while established plants can tolerate severe defoliation. Removing the adult beetles by hand is the recommended control. Beetle numbers usually decline by early to mid-July. CUTWORMS - Several CSA growers have reported cutworm infestations primarily impacting greenhouse plants this month. Cutworms are active throughout the summer, but are rarely a problem after spring. Problems can be reduced by placing aluminum foil or cardboard collars around transplants to create a barrier that stops cutworm feeding. If damage or larvae are discovered, the cutworms should be physically removed and crushed or dropped into soapy water. SQUASH BUG - Adults are appearing on cucurbits in home gardens, and populations generally increase sharply by mid-July with the addition of small nymphs. An average of one egg mass per plant when plants are flowering is recommended as the basis for initiating treatment. For gardens, hand picking and destroying the bugs and their eggs is most effective. Another option is to place cardboard or newspaper on the ground next to the plants. At night the squash bugs will aggregate beneath the cardboard and can be destroyed in the morning. Organic growers may use directed applications of pyrethrum (PyGanic) or the pre-mix with azadirachtin (Azera). Growers should be aware that the efficacy of most insecticide materials is reduced at temperatures above 80°F and the smaller nymphs are more easily killed than the adults. Refer to UWEX publication A3422 "Commercial Vegetable Production in Wisconsin" for a list of registered insecticides. CABBAGE CATERPILLARS - Low to moderate infestations of diamondback moths and imported cabbageworms are prevalent in southern and western Wisconsin community gardens. The larvae of these cabbage pests feed on leaves and cause large ragged holes, eventually infesting the developing heads of broccoli, cabbage and cauliflower. Treatment thresholds are reached when 10% of cabbage in the early heading to mature head stages are infested, or 10% of broccoli and cauliflower in the first flower or curd to maturity phase are damaged. Cole crop growers are reminded that imported cabbageworms, diamondback moths and cabbage loopers are considered to be a single caterpillar complex, and the same infestation threshold applies to all three species. Bacillus thuringiensis (Bt) and chemical insecticides are effective controls for small caterpillars. -- Krista Hamilton, DATCP Entomologist 
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