Timing Black Cutworm Scouting

Once again, we urge you to view the “Black Cutworm Pheromone Trap Report.” For the fifth consecutive week, our volunteer trappers have been busy counting captured moths, e.g., lots of intensive captures. On April 1, after severe storms arrived in the state, the trappers were detecting “moth-ageddon.” There was panic at first, then fear. But, as we have seen in the past, these captures are more like an alert to start scouting, than they are an indication of certain pressure and damage.

However, what is certain is that conditions recently have been favorable for these “fair-weather pests”; they are not very freeze-tolerant as larvae. Due to a lack of widespread hard freezes since then, we initiated heat unit (50°F base) accumulations (“biofix”) to determine their rate of development, see accompanying state contour map below.

Back in the mid-1970’s, researchers* from the University of Illinois published the approximate heat unit accumulations for each life state of the black cutworm, see pictures below. Although these data are almost 50 years old, there is no reason to think that the amount of heat units required for larvae to develop has changed since then. Take a look at the chart below, and compare with the map at bottom – at this time of year, the part of the state where you are planning scouting matters a great deal.

 

Cumulative Degree Days Black Cutworm Stage Activity
0 (biofix) Intensive moth capture Egg laying
90 Hatch
91-311 1st – 3rd instar larvae Leaf feeding
312-364 4th instar Cutting initiates
365-430 5th instar Cutting
431-640 6th instar Cutting
641-989 Pupa to moth Pupation in soil
*modified from Luckmann et al., Journal of Economic Entomology, June 1976

 

From the previous moth captures, the heat unit (50°F) accumulations since biofix, and the above development table, you can now better time your scouting trips for high-risk emerging corn (i.e. when black cutworms are likely to be large, and corn is small, and there is nothing else for them to eat!)

Remember this: lots of black cutworm moths does not an outbreak make! Without a litany of ecological/biological/meterological reasons why, let’s just say that it takes a “perfect storm” of variables for black cutworm to survive and damage to our crops. Stay tuned!

As of May 3rd, cutting from black cutworm is possible in extreme southern Indiana.

As of May 3rd, cutting from black cutworm is possible in extreme southern Indiana.

 

The following graphics may help in recognizing black cutworm and their damage:

Black cutworm eggs and newly hatched (1st Instar) larvae.

Black cutworm eggs and newly hatched (1st Instar) larvae.

 

Size comparisons of 2nd to 6th instar black cutworm larvae.

Size comparisons of 2nd to 6th instar black cutworm larvae.

 

Early instar leaf feeding, the small larva may be in the folds of the leaf or in the soil.

Early instar leaf feeding, the small larva may be in the folds of the leaf or in the soil.

 

Newly cut seedling and larva revealed by carefully digging around the plant. Note the new growth of this delayed, but not dead, seedling.

Newly cut seedling and larva revealed by carefully digging around the plant. Note the new growth of this delayed, but not dead, seedling.

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