These butterflies have both a white and yellow form. Alfalfa fields in bloom attract very large numbers of these butterflies. The caterpillar of the alfalfa butterfly can be a pest of the crop, but rarely is abundant enough in ND to cause concern. Most of the aphids captured this week are those associated with small grains but green peach aphids were found at most locations. As small grains mature throughout the Valley a greater proportion of aphids will develop wings.
Winged aphids leave small grains in search of a suitable host.
Minnesota and North Dakota locations averaged 8.45 aphids per trap of all species and 0.17 green peach aphids per trap. We continue to find green peach aphids on wild mustard. Wild mustard is growing profusely in many drowned out row crops. If these wild mustard infested fields persist, we would expect to capture green peach aphids throughout the month of August, which is not good news for seed potato growers. If the green peach aphid flight activity patterns observed in 1998 and 1999 are repeated in 2000 we will see a marked increase in green peach aphid flight activity within the next two weeks.