Corn flea beetle and
Stewart's wilt predictions for 2001
Mike Hoffmann, Tom Kuhar & Jeff Gardner, Dept. of Entomology, Cornell University, Ithaca & Lee Stivers, NY Crop Research Facility, Batavia
Stewart's wilt
is an important disease of sweet corn in New York. The disease is caused by a bacterial pathogen that is vectored
almost exclusively by the corn flea beetle.
The bacteria overwinter in the gut of adult flea beetles. In the spring, beetles infest early
plantings of corn and transmit the pathogen to the plant by feeding and
defecating on leaves. Stewart's wilt
is characterized by development of conspicuous streaks on the leaves and stalk
due to plugging of vascular tissue.
Early wilt infections cause reduction of yield by reducing stands due to
death or stunting of infected seedlings.
Seedlings, which survive early infections, remain stunted, tassel
prematurely, and frequently produce no ears or nubbins. Disease severity is aggravated by high
temperatures, which causes faster development and movement of the bacteria
through the infected plants.
Corn flea
beetles spend the winter as adults near the soil surface in grassy areas in and
around cornfields. Severe winter
temperatures can kill most of the population and result in a very low incidence
of Stewart's wilt disease the following summer. Thus, a winter
temperature index is used to predict the likelihood of Stewart's wilt
problems. The forecast is based the sum
of the mean monthly temperatures for December, January, and February. The Stewart's wilt index (likelihood of wilt
problems) is as follows:
>100 = severe
90-100 =
moderate - severe
85-90 = moderate
80-85 = light
<80 = absent
2001 forecast: The Stewart's wilt index
for several New York locations can be found below.
According to
the Stewart's wilt index forecasting model, the 2000-2001 winter temperatures
were sufficiently cold to kill most of the corn flea beetle population in New
York.
For much of the state, the Stewart's wilt index falls into the "absent" category (cumulative monthly temperatures below 80). Notable exceptions include some areas along the Hudson Valley and Long Island, where the Stewart's wilt forecast is considered to be "light" to “mod-severe “ for Suffolk Co. We do not anticipate serious Stewart's wilt problems in sweet corn in 2001 for most of the state.
However, based
on our experience with this forecasting program, this does not necessarily mean
that Stewart's wilt will be completely absent from the area in 2001.
This spring, we
will be monitoring corn flea beetle population levels and assessing Stewart's
wilt incidence in the summer in numerous fields throughout central and western
New York to validate the predictive accuracy of the Stewart's wilt index. We are also currently refining the Stewart's
wilt model to include additional variables such as, snow cover, number of days
that temperature dropped below 0 degrees F, planting date, and susceptibility
level of the sweet corn variety.
Management options for Stewart's wilt
disease control include:
1) planting
resistant varieties
2) planting with Gaucho-treated seed (EPA Section 18 label for 2001) for susceptible varieties
3) applying a
foliar insecticide spray to protect seedling corn if needed
We are still
recommending that susceptible varieties of sweet corn be commercially treated
with Gaucho.
| Cayauga | Locke | 67 | abs |
| Chautauqua | Jamestown | 72 | abs |
| Chenango | Norwich | 71 | abs |
| Dutchess | Poughkeepsie | 77 | abs |
| Franklin | Malone | 49 | abs |
| Fulton | Gloversville | 63 | abs |
| Jeffrson | Watertown | 59 | abs |
| Livingston | Avon | 77 | abs |
| Niagara | Buffalo | 76 | abs |
| Oneida | Camden | 64 | abs |
| Ontario | Geneva | 75 | abs |
| Rensselaer | Melrose | 69 | abs |
| Schoharie | Cobleskill | 69 | abs |
| St. Lawrence | Canton | 53 | abs |
| Suffolk | Islip | 92 | mod-sev |
| Sullivan | Bloomingburg | 76 | abs |
| Tompkins | Ithaca | 73 | abs |
| Ulster | Gardiner | 81 | light |
| Washington | Whitehall | 67 | abs |
| Wayne | Ontario | 82 | light |
| Westchester | Yorktown Hts. | 83 | light |
| Wyoming | Warsaw | 63 | abs |