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ISSUE 15  August 15, 2002

 

SOYBEAN APHID SITUATION

Many fields in the region are in the R5 to R6 growth stages. The risk of yield loss to soybean aphid should be passed based on field research from last year. Several people from around the region have reported some rapid increase of aphid numbers in isolated fields. However, the fields are in these advanced growth stages and losses are not expected.

Winged aphids and nymphs with wing buds are present. The proportion of the population that is or will be winged was between 25 to 50% in some fields this week. We would expect these numbers to continue to increase.

Predator insects are abundant wherever aphids are found. It has been very easy to find the multicolored Asian lady beetle, Harmonia axyridis, during the past week. This lady beetle larva is "alligator-shaped" and black with two yellow stripes along the sides. Lady beetle larvae move rapidly over leaves and branches, eating aphids and other soft-bodied insects. Their eggs are yellow, oval shaped, and laid in clusters of about 20, usually on the undersides of leaves.

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Larva of the multi-colored Asian lady beetle

 

U OF MINNESOTA APHID ALERT

Aphid Situation in Week Ending August 9 the following is from Dr. Ted Radcliffe, Entomologist, U of Minnesota, and is available on the internet at:

http://ipmworld.umn.edu/alert.htm

Flight activity of aphid vectors of potato viruses remained high during the week ending 9 August. Although bird cherry-oat aphid, Rhopalosiphum padi captures declined this week by 24%, turnip aphid, Lipaphis erysimi, flight activity remained strong. Turnip aphid flight activity increased 1.5-fold compared to the previous week and comprised 67% of the total aphid capture. Current season spread of PVY has been reported on some potato fields. Plants with current season infection will serve as secondary inoculum sources that can further increase inoculum pressure for the region. Consequently, the risk of PVY transmission remains high for the Red River Valley.

Flight activity of green peach aphid, Myzus persicae, also increased 11% this week to 0.38 aphids per trap. It is important to note that the capture of 1 aphid per trap in a week corresponds to approximately 1 aphid per plant per day. Therefore, intensive scouting of seed potato fields for green peach aphids is extremely important and initiate treatment immediately when the threshold of 3 green peach aphids per 100 leaves has been reached.

The ripening and harvest of small grains are also associated with immigration of aster leafhoppers, Macrosteles quadrilineatus, into potato fields. Aster leafhoppers do not reproduce on potato so only the adult stage is found on potato. There is no evidence for aster leafhoppers causing direct feeding damage and hopperburn on potato but they can be important in transmitting the pathogen (not a virus) of the disease known as purple top or haywire. Purple top is especially important in processing potatoes because it is implicated as a possible cause for darkened chips. Aster leafhopper has the typical wedge-shaped body of leafhoppers but the body of aster leafhoppers is dull green, compared to the bright lime green color of potato leafhoppers, with two rows of three black spots on the top of the head. However, when disturbed, the large numbers of highly mobile aster leafhopper adults can create the illusion of heavy potato leafhopper invasion.

In order to avoid unnecessarily treating aster leafhoppers sample 35 mid-plant leaves in each of the four locations throughout the field to determine if potato leafhopper immatures (nymphs) are present. Potato leafhopper nymphs are wingless, rod-shaped, 1-2 mm in length, with lime green colored bodies. The nymphs run characteristically sideways when disturbed. The threshold density to initiate treatment for controlling potato leafhoppers in potato is one nymph per 10 leaves. Fortunately, most insecticides provide good control of potato leafhoppers but chemistries and rates need to be chosen with caution to avoid flaring aphids. Our results suggest that effective control of potato leafhoppers can be achieved without flaring of aphids with the use of low rates of Asana (1.2 fluid oz/acre) and Dimethoate (4 fluid oz/acre) applied at threshold densities.

 

MUSTANG USE EXTENDED IN FLAX FOR GRASSHOPPER MANAGEMENT

Jim Gray, Pesticide Registration Coordinator, ND Department of Agriculture, has provided information on the extension for using Mustang in flax to control grasshoppers.

The crisis exemption issued earlier was for July 30 to August 13. Following the crisis exemption (issued by ND Dept Ag), there was a request made for a specific exemption (Sect 18 Emergency Exemption - EPA) for use of Mustang insecticide in flax. Under these circumstances, the use under the crisis exemption is allowed beyond the original 15-day use window.

The new use period has been extended to September 30. A copy of the revised label is available at:

http://www.ag.ndsu.nodak.edu/aginfo/pesticid/pesticid.htm

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu


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