Being early March, it is time to put out the annual corn flea beetle and Stewart’s leaf blight prediction based on the average temperatures the past three months (Dec, Jan, and Feb.). Stewart's bacterial disease is dependent on the level of bacteria-carrying flea beetle survival over the winter. Because higher populations of the flea beetle survive during mild winters than during cold winters, winter temperatures have been used to predict the risk of Stewart's disease. Compared to recent years, and even the past few decades, the past three months have definitely been on the cold side.
The 'flea beetle index' is calculated as the sum of the average temperatures of December, January and February. This winter we find that all areas of the state have indexes less than 90 suggesting that the risk for the insect and the disease is negligible. Only the two most southern locations (Piketon and Jackson) even reach an index over 80, coming in at 84.8 and 88.7, respectively. The other locations and the corresponding indexes are: Wooster (OARDC) 73.8, Ashtabula 67.5, Hoytville (Northwest Research Station) 63.2, and South Charleston (Western Research Station) 74.1. Obviously, this was a very cold winter!
As always, we would recommend that growers still scout for flea beetles, especially if they have planted a hybrid that is susceptible to Stewart's disease. It is always better to be on the cautious side. However, the realization is that most field corn planted these days, especially all transgenic hybrids, already come with an insecticide seed treatment applied. Thus, it is mostly non-transgenic corn that might need to be considered and watched more closely. Also, field corn hybrids tend to be more resistant to wilt than sweet corn. Sweet corn varieties are much more susceptible to wilt in the first leaf stage. A few are resistant by the second leaf stage and many are resistant in the third and fourth leaf stage. Consult your seed supplier for information on resistant varieties and hybrids.