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Forages & Grains
Volume 52 Number 5 Date 05/11/2007 Insect development in alfalfa has escalated sharply and populations are reasonably high for this time in May. Among the most common insects detected this week were alfalfa weevil adults and larvae, tarnished plant bug adults, alfalfa plant bug nymphs, pea aphids, planthoppers, meadow spittlebug nymphs, springtails, bean leaf beetles, alfalfa caterpillar butterflies, clover leaf weevil larvae, and an assortment of beneficial species. The sum of insects active in alfalfa is already too high to count accurately in 50 sweeps. Reducing the number of sweeps to 20 or less is advised, although the sets of sweeps taken should be increased accordingly (five sets for a total of 100 sweeps). Alfalfa weevil - Surveys in Rock and Walworth counties revealed high numbers of first and second instar larvae as well as evidence of tip feeding injury. Counts of larvae hatched from overwintered eggs range from 9-23 per 25 sweeps, while adult weevils average 2 per 25 sweeps. With most alfalfa fields still days away from flowering, it appears damage to first crop hay is a distinct possibility. Under the present weather conditions, individual females may deposit roughly 60-70 eggs per night. Look for larval populations to surge in the next week. Potato leafhopper - Migrants appeared this week in low numbers. The first individuals were spotted at a porch light in Columbia County on the evening of May 9, but not in the Rock and Walworth County fields surveyed earlier in the day. Like other migratory species, this insect passes the winter in the Gulf States and is directed into Wisconsin on strong southerly winds each spring. In some years, migrating leafhoppers seem to arrive overnight and build to outbreak levels in a matter of days. Meadow spittlebug - Spittle masses are becoming more common. Nymphs are still very small, most are in the first or second instar stage of development. It is still too early to determine the degree of infestation, although some alfalfa fields had one nymph per 10 stems. The action threshold for meadow spittlebug is one nymph per stem. Pea aphid - Pea aphid hatch began on April 24 and the earliest hatched aphids are now mature. Some fields contain up to 19 aphids per 25 sweeps. Reproduction has begun in the southern counties. Populations in the Portage County area are lower, averaging three per 50 sweeps. Tarnished plant bug - Adults were noted in alfalfa fields again this week, but still no nymphs have been observed. Sweep nets counts of adults numbered fewer than five per 25 sweeps. Freeze injury to winter wheat - The northeast and north central areas of the state showed some severe freeze injury to winter wheat following an untimely winter storm in early April. Negligible to moderate injury was noted in all other regions. Freeze injury estimates for the nine agricultural statistics districts are provided in the map below, courtesy of the USDA, NASS, Wisconsin Field Office. -- Krista Hamilton 
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