As we have indicated many times in previous issues of the Bulletin, densities of potato leafhoppers in Illinois have been incredibly large this year. I still receive reports from people who have witnessed "clouds" of these pests during sporting or entertainment events held at night. And the numbers of potato leafhoppers in alfalfa fields reflect these observations. Leafhoppers also have caused some injury at the edges of soybean fields. Therefore, it is very important that you don't confuse the symptoms of injury caused by potato leafhoppers with injury caused by twospotted spider mites. |
Soybean leaf injured by potato leafhoppers.
Injury to soybean leaves caused by potato leafhoppers usually first appears along the edges of the leaflets and is similar in appearance to the classic "hopperburn" symptom in alfalfa. The edges of injured leaves often curl and turn brown. Severely injured leaves may change from green to yellow to brown. Severely injured plants may become stunted. Initial injury to soybean leaves caused by twospotted spider mites appears as small, yellow or white spots called stipples. As the level of injury increases, the stippling becomes widespread over the leaf. Severely injured leaves will show signs of leaf water stress. Injured leaves turn from yellow to bronze to brown, and dead leaves eventually drop off the plant. Severely injured plants may become stunted.
As is almost always the case with insect injury to crops, the presence of the insect (or mite) usually tells the tale. You should find webbing associated with infestations of spider mites, and you should be able to find the mites. If you can't find them on injured plants, look for them on nearby healthy plants. You should also be able to find leafhoppers, either nymphs or adults, if they are causing the observable problem. Remember, accurate diagnosis is very important if you are trying to make a decision about treating with an insecticide or miticide.--Kevin Steffey