Guessing the answer to the Wheel of Fortune word puzzle without all the letters on the board may win you money, but guessing about vegetable diseases could well put a pest control adviser (PCA) and the producer he works for in the poor house.
University of California Monterey County Farm Adviser Steve Koike told PCAs at the recent Bayer CropScience consultants seminar in San Diego that guessing is being slipshod and “you cannot afford to be sloppy in the vegetable business” where the intense cropping pattern of up to four crops per season on the same acre in California coastal vegetable production does not allow for guessing.
“You can have a crop like baby spinach in production in as little as 18 to 22 days,” said the veteran plant pathology farm adviser.
Extremely high quality standards, as well as a diversity of products from whole plants to bagged and clipped products, also pose a challenge to PCAs who cannot afford to guess at which disease is damaging a crop. “Vegetables have a very low market-tolerance for disease or phytotoxicity,” he reminded PCAs.
Changes in production practices are another reason guessing is not good. For example, Koike said the move to drip irrigation and 80-inch beds to increase production also creates more pressure from a wide array of diseases he said can occur every year and during any month.
“Accurate and timely diagnoses are required,” he added. “If you don't know, send a sample to the lab for diagnosis. If you think you know, send the sample anyway for confirmation.”
There are no true disease eradicants. All disease treatments are preventative. “Stay ahead of the game. If you see a disease, it is too late.”
There is a good selection of fungicides available for vegetable disease control. However, products are fairly specific to one or only a few diseases. “There are no general fungicides for all diseases,” he said.
Multiple sprays are needed to protect newly forming tissue, which can be a challenge scheduling around field work. Multiple products are recommended to counter resistance of a pathogen.
“Fungicides are not usually applied alone. A tank mix with an insecticide is common, which can compromise a fungicide treatment,” he explained.
Scheduling is also challenging because fungicide treatments are not normally based on crop state or models. Adjacent crops create additional concerns when applying crop protection chemicals.
The expansion of quick-growing crops like baby vegetables create re-entry and pre-harvest interval concerns. Intense crop rotations make plant-back restrictions an ever-present concern.
Resistant cultivars are often a first line of defense against diseases. However, these “come and go, making fungicides a critical tool for disease control.” The need for new fungicides will be ever present with the discovery of new races, new pathotypes and fungicide resistance.
For example, Koike used the following statistics to explain how a disease like downy mildew can be a moving target due to new races:
|Treatment/rate/acre||DM Lesions||% Infection|
|Maneb 2 lb. (4x)||9.0||90|
|Aliette 4 lb. (4x)||7.7||100|
|Reason 0.043 gal (4x)||3.1||72.5|
|Previcur 0.188 gal +|
|Reason 0.022 gal (4x)||1.7||50|