Onions - In 2006, onion growers experienced high populations of onion thrips (Thrips tabaci). Hot and dry conditions during mid summer contributed to elevated onion thrips populations. So far in 2007 we have observed increases in daytime average high temperatures coupled with below average rainfall increasing the chance of early onion thrips populations. A few adult onion thrips have been observed in the past 2 weeks upon recently emerged, direct-seeded onion. Populations of onion thrips are moving in from overwintering hosts into onion at this time and are often initially highest along the field borders, near woods or in the vicinity of grain or field crops.

 

 

Damage results from feeding by both adult and immature thrips. Thrips extract the contents of epidermal cells leaving them empty and necrotic resulting in ‘silvering’. Chemical control of the onion thrips is presently the most consistent management measure. Earlier this month, Wisconsin received approval from the EPA for a Section 18, Emergency Exemption for the use of Carzol SP. Product in Wisconsin is available from the following suppliers:

Yellow sticky traps can be used for monitoring the migration patterns of adult onion thrips from their over wintering hosts but are not informative regarding the decision to spray. Once the migration has begun, individual onion plants in several sections of the field should be inspected on a regular basis. Early in the season, surveillance and monitoring can be focused on the outer rows of plants with in the field where developing populations are first detected. Leaves must be parted to reveal the youngest emerging leaf in the center of the plant where immature thrips can be counted. Thrips prefer this area because it is the most succulent part of the plant and provides excellent protection from weather and insecticides. Adult thrips may also be found on older leaves, particularly where leaves have folded over, providing a sheltered area.

Cabbage - Insect pressure in transplant cabbage is very light at the Arlington Agricultural Experiment Station (AES). None of the important Lepidopterous insect pest species including imported cabbageworm, diamondback moth, or cabbage lopper have been reported infesting transplant cabbage in the 5 to 7 true leaf stage. A few springtails have been observed on recent transplants and light infestations pose little threat to a well-established stand.

Snap Beans - Populations of soybean aphid were first detected last week (May 21-25) by Dr. David Hogg, Department of Entomology, in an experimental soybean plot at the West Madison, AES. Among 60 visually inspected plants, 3 had a single adult (alate) plus a few nymphs and another 5 had only nymphs resulting in13.3% (8/60) of the plants infested. A total of 41 nymphs were counted, for a mean of 0.68 per plant. Most aphids were found on the unexpanded leaf tissue. The soybean aphid has been implicated in past increases in Cucumber mosaic virus (CMV), Alfalfa mosaic virus (AMV), and other problematic viruses in processing snap beans and has more recently been documented as a competent vector of several nonpersistently transmitted viruses. Unfortunately, insect vector control using insecticides has limited effectiveness in reducing spread of nonpersistent virusesinto susceptible crops.

Potato – Overwintering Colorado potato beetle (CPB) adults have been emerging over the last two weeks (May 13-26) and colonizing newly emerged potato fields. The adult CPB overwinters in the soil along field margins near windbreaks and other wooded areas surrounding potato fields, as well as in the field.  These adults have begun to feed, mate and lay clusters of 10 – 30 yellow eggs on the underside of the newly emerged potato leaves. Females typically lay 350 or more eggs during their lives and they will last for 4-6 weeks during the early part of the season. Egg masses at different stages of development have been observed ranging from recently laid, bright yellow egg clusters to darkened orange masses nearing hatch. Egg hatch and emergence of 1^st instar larvae from the earliest egg masses is expected very soon at the Arlington, AES.

Dead adult beetles have been observed in furrows at both the Hancock and Arlington AES signaling the effects of the systemically applied, nicotinyl insecticides. For growers who have not used an at-plant, systemic nicotinyl insecticide, plans should be made for the timely use of reduced risk materials targeting early instar larvae to include, but not limited to, spinosad (Spintor^® 2SC), abamectin (Agrimek^® 0.15EC), novaluron (Rimon^® 0.83EC), thiamethoxam (Actara^®), imidacloprid (Provado^® 1.6F), and Bacillus thuringiensis subsp. tenebrionis.