This week, 22 of 232 soybean fields sampled by the MDA were found with soybean aphids. The percentage of plants infested was low - most fields had only 1-2 plants out of 30 infested. A few fields in southern MN had 6-8 plants out of 30 infested. About half of the fields with aphids had 1 plant infested with > 100 aphids. No fields were found with more than 1 plant at this level.

Low numbers of bean leaf beetles (1-2/30 sweeps), as well as green cloverworm and loopers can be found in soybeans throughout southern Minnesota. Light levels of imported longhorn weevil can be found in some fields in southern MN. Low numbers of thistle caterpillars were found in two fields in the NW. Grasshoppers are generally present in low numbers in soybeans although a total of four fields were found this week with 0.5 - 1 grasshoppers/sweep (Goodhue, Traverse, Morrison and Norman Counties). Despite the higher grasshopper numbers in some fields, defoliation was light in all fields sampled this week.

Aphids in alfalfa

Like aphids in small grains, pea aphids in alfalfa also increased dramatically during the past week. This increase has occurred throughout the state (Figure 12). Potato leafhopper was at economic levels (2 / sweep) in some fields in the SE this week (Goodhue, Dodge, Wabasha and Houston Counties). Alfalfa plant bug is also numerous in many fields throughout the state.

Corn rootworm emerging in south

Northern corn rootworm adults were found in 22 of 209 corn fields as well 13 of 232 soybean fields inspected this week. Beetles were present in low numbers (1-2 / 30 sweeps) in soybean but in higher numbers in corn (up to 28 per 30 plants in Blue Earth County (SC). Western corn rootworm was also found in corn in the SC but in fewer fields (11 of 209) and in lower numbers (1 - 6 / 30 plants). No western corn rootworm were found in soybean.

Corn is tasseling in the south and some fields are beginning to silk. Look for corn rootworm numbers to increase as more fields begin to silk.

European corn borer  

European corn borer activity continues to be low and predominantly found in the southeastern quarter of the state. An egg mass was found in one field in Otter Tail County (WC) and one field in Morrison County (C) this week, presumably from univoltine Ecb. Larvae were found in fields throughout southeastern Minnesota - most were in the 2nd and 3rd instar.

Aphids, etc. on increase in small grains

Aphids numbers increased several fold this week in small grains, particularly in the NW (Fig 7). The primary aphid species in the NW appears to be the greenbug. Aster leafhoppers have also become very abundant in the northern half of MN with numbers reaching 10+ / sweep. Moreover, relatively high numbers of armyworms were found in some small grains this week (Fig 8). Most fields sampled this week in southern MN were near maturity while fields in northern MN were less far along in development.

Diseases of wheat

Only three wheat fields were found with scab this week, only 1 plant was infected in two fields, 25 plants were infected (low severity) in the third field. Bacterial stripe was found in many fields in the NW this week. Leaf rust, tan spot / Septoria and loose smut were again commonly found throughout western MN during the past week at levels similar to previous weeks.