Insects in Cover Crops

2018 Crop Production Clinic Proceedings

Insects in Cover Crops January 8, 2018

Ryer cover crop
Figure 1. Rye cover crop planted in small section for soil erosion. Center of photo shows the absence of cover crop and normally developing corn plants.
Wheat stem maggot damage in corn
Figure 2. Wheat stem maggot damage on corn plants with (a) dead heart symptoms and (b) excessive tillering.
Wheat stem maggot life stages
Figure 3. Wheat stem maggot larvae (a) found in damaged corn plant, adult reared from whole plant sample (b) and egg on wheat leaf (c).

Cover crops are becoming increasingly popular in crop production systems as a means to reduce soil erosion, increase soil organic matter, conserve nitrogen, and suppress weeds. Integration of cover crops into a cropping system can potentially alter insect activity and abundance by

  • increasing beneficial insects (predators, parasitoids),
  • harboring potential pests that may damage the subsequent cash crop, and
  • creating new pests as a result of a green bridge between a cover crop and cash crop.

Insect pests that have been associated with cover crops include

  • green cloverworm,
  • Japanese beetle,
  • bean leaf beetle,
  • stink bugs,
  • true armyworm,
  • black cutworm,
  • seed corn maggot, and
  • wireworms.

Beneficial insects reported in cover crop studies are

  • ground beetles,
  • lady beetles,
  • hover flies, and
  • spiders.

Insect activity and impact on a subsequent cash crop is complex due to the interaction of a number of different factors such as

  • cover crop species, planting date, and method of termination;
  • timing between termination of cover crop and planting cash crop;
  • environmental conditions; and
  • cropping history.

In 2017, wheat stem maggot was found damaging early-season corn planted into wheat or rye cover crops in central and eastern Nebraska.

  • In all cases, damaged fields had a cover crop that was still alive at the time of corn planting
  • In some cases, small portions of fields were planted to a cover crop (Figure 1). In such situations, infested and damaged plants were confined to these areas occurring within 1-2 feet of the cover crop.
  • From 2% to 30% of corn plants in fields were damaged, showing dead heart symptoms (Figure 2a) and excessive tillering (Figure 2b).
  • Dissection of damage plants revealed larvae ranging from 3-6 mm in size (Figure 3a).
  • Whole plant samples were collected and larvae were reared to adult for species identification.
  • Little to no information is available on wheat stem maggot in cover crops.
  • Greenhouse studies on corn infested with wheat stem maggot adults (Figure 3b) and eggs (Figure 3c) have not resulted in significant damage to corn plants, suggesting that infestation occurred as a result of larval movement between cover crop and corn.