2014 University of Minnesota Cooperative Black Cutworm Trapping Network

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1 2014 University of Minnesota Cooperative Black Cutworm Trapping Network Report #3 Week of April For more information: May 1, 2014 The report from 1 year ago mentioned a winter storm warning. The results were unfortunate indeed for a large portion of Minnesota east and south of Mankato. Again this year spring seems unable to read the calendar. For the week of April we have more thunderstorm events and more cutworms. The wind was hard on some of the traps in WC MN. If your trap is damaged by wind, animals or accidentally being glued to your fore head we have some spares. explain how we use degree days to do so. None of the reporting traps had significant captures. There will be at least two locations in next week's report where 2 night captures were more than eight /night. Also in the next black cutworm report, we will start making cutting predictions and

2 Some folks insist on panicking early. I am hearing some folks are encouraging at plant insecticides for black cutworm. The nice thing about black cutworm is we can treat only where problems occur. Predicting problems is the purpose of this network and using an insurance insecticide for black cutworm defeats the purpose. Please submit your trap capture results on Friday.. We would appreciate hearing about it earlier when your trap captures more than 8 moths in a 2 night period! Good luck! Bruce Potter and Travis Vollmer Black and other cutworms in Minnesota corn Black cutworms are not the only cutworm species than can injure crops in Minnesota. As corn (and other row crops) germinate and begin to emerge they can be attacked by several species of cutworms. Table 1 lists some of the most common species that might be found in Minnesota corn fields. Most species can overwinter in Minnesota as eggs or larvae. Black and variegated cutworms cannot winter here and migrate into the state each spring. While we can project cutting dates for the black cutworm, corn should be scouted for other cutworm species as soon as it emerges. Because cutworms that overwinter, particularly those that winter as larvae, begin development before migrant black cutworms arrive, they are ready to feed on corn early. Often, the first corn leaf feeding observed in the spring is from overwintered dingy cutworm larvae. Table1. Some common cutworms of Minnesota Species Eggs laid # gens. Overwinters as Likely habitat Black Spring-summer 3 Adults migrate Late tilled fields, early broadleaves Bronzed Fall 1 Eggs/Larvae After sod Clay-backed Fall 1 Larvae After sod Darksided Fall 1 Eggs Dingy Summer-Fall 1 Larvae After sod and alfalfa, weedy fields Glassy Summer-Fall 1 Larvae After sod Redbacked Fall 1 Eggs Light/medium textured soils Sandhill Summer-Fall 1 Larvae Sandy soils Variegated Spring-summer 2 Adults migrate After alfalfa, weeds Certain species prefer particular habitats. For example, sandhill cutworms are found in sandy soils and several species tend to be problems in crops planted into sod. Dingy cutworms are often abundant when corn is planted after alfalfa or fields that were weedy the previous year.

3 Species ID is important to determine damage potential. Small larvae of all species feed on weeds and leaves and cannot cut corn. Dingy and variegated cutworms are primarily leaf feeders feeding at or above the soil surface. Consequently, they don t usually cut corn below the soil line and growing point and the plant recovers. However, the larvae of some species like glassy, sandhill and black cutworms tend to feed below ground at or below the growing point. This tendency for feeding to kill corn plants makes black cutworm a threat. When larger larvae tunnel into the growing point, corn as large as 5 or 6 leaves can be killed. Fortunately, damaging black cutworm populations are infrequently encountered. Pictures of some of these cutworm species can be found at Northern Plains IPM site Some excellent comparison images of black and dingy cutworms are available at the University of Nebraska s website With a bit of practice, the two species are easily distinguished by the size of paired black bumps (tubercles) on the top of each segment. These tubercles are unequal in size on the black cutworm. What make a corn field high risk for black cutworms? Tillage and crop rotation The overwintering cutworm species lay eggs based on soil type and previous year s vegetation. Black cutworm moths arriving in Minnesota seek out areas with crop debris, sheltered areas and low spots in the field to lay eggs. Early season weed growth is very attractive to the moths and winter annuals (e.g. shepard s purse) and early spring broadleaves (e.g. common lambsquarters) patches in fields are often infested. The moths are not attracted to spring tilled fields. Unworked fields, or fields with reduced tillage where more crop debris is on the surface, attract more egg laying moths. The higher risk of black cutworm attack in conservation tillage can be seen in tillage plots at the Southern Research and Outreach Center in Waseca in 1985 (Fig 1) and 1986 and the Southwest Research and Outreach Center in 2001 (Table 2) Table 2. Black cutworm damage among tillage systems Waseca, 1986 Lamberton, 2001 Fall MB plow/ Spring Fld. Cult. 5.0 Fall Chisel Plow/ Spring Fild. Cult c Spring Field Cult. 3.0 c Ridge Till ab No Till c Fall Strip Till 4.0 bc Spring Strip Till 9.2 a

4 Fall tillage that buries crop residue and spring tillage eliminates early spring weed growth before the flight arrives and reduces the risk and severity of black cutworm attack. Historically, soybean residue is more attractive than corn but this may be partially due to the amount of fall tillage or to species and numbers of broadleaf weeds in the seedbank between the two crops. Tillage after egg laying generally has little impact on either egg or larval survival, unless the field is kept black for a couple weeks after egg hatch, long enough to starve the larvae but a yield avoiding planting strategy. Fig. 1 Influence of tillage and previous crop on black cutworm damage in Soybean Corn Mold Board Chisel Ridge Till No-Till BT Hybrids, seed applied and at plant insecticides Some folks are adding a soil insecticide to Bt-RW corn in areas with Bt-resistant rootworm populations. That is an entirely separate issue than cutworm management. Soil applied at-plant insecticides can provide control of cutworm larvae. However, they are not recommended as insurance applications for two reasons. At planting, it is difficult to predict which individual fields will have economically damaging cutworm infestations. Secondly, post-emerge insecticide rescue treatments work very well. T-band applications for granular insecticides, if so labeled, are sometimes more effective on cutworm than in-furrow applications. However, the banded insecticides are not necessarily more effective on corn rootworm. Be cautious of potential interactions between organophosphate (counter is an example) and some herbicides. Always read the pesticide labels and use the appropriate rates. Incorporate the insecticide bands as indicated on the label. Windy planting conditions reduces the accuracy banded

5 applications when not incorporated. Later blowing of loose dry soils can also reduce efficacy of non- incorporated bands. High rates of neonicitinoid seed treatments (e.g. Poncho, Cruiser, Gaucho) are very effective on many seed and seedling insects and they can provide some protection against black cutworm. They may not always provide satisfactory control. Bt hybrids containing the Cry 1F protein (Herculex /HX1) or Vip3a protein (Viptera), alone or in stacks, are labeled as controlling black cutworm. While they reduce risk, they might still be damaged as observed in some 2012 fields. An at-plant insecticide is probably not that helpful for cutworms when added on these hybrids. Remember, the Cry 34/35 Ab1 (Herculex RW protein) is not the same as the Cry 1F above-ground protein. Large numbers of late-instar cutworms moving from weeds to take a bite of corn can overwhelm the neonicitinoids or Bt in corn tissues. There has been no evidence of black cutworm zombies. Therefore, you should only need to kill a cutworm once. A Bt hybrid with the insecticide treated seed and with an added insurance at-plant insecticide would be trying to kill a cutworm three times - even before you knew if moths landed nearby. A little over prepared, perhaps? Scouting and rescue insecticides applications are still the best defense against yield loss from black cutworms if problems occur.