Gordon Johnson, Extension Ag Agent, Kent Co.; firstname.lastname@example.org
Vegetable and fruit growers would rather have a dry year than a wet one. Keeping irrigation going might be a problem in the dry year, but vegetable and fruit crops have better quality and disease control is much less challenging. The following are some observations from this season.
● Disease pressure is very high with wet weather diseases being a major problem. Pythium rots in seeded and transplanted crops, Aphanomyces root rot in peas, late blight in potatoes and tomatoes, downy mildew of cucurbits, downy mildew of grapes, Phytophthora blight in cucurbits, gummy stem blight in melons, blossom blights and Botrytis on fruits, and numerous other diseases favored by wet weather are active in the region this year.
● Scheduling processing crops has been a challenge in 2009 and plantings have had to be juggled and moved around to account for fields too wet to plant.
● Peas have been hurt badly by the wet weather. Root rot is a major problem along with drowned out areas, extra weed pressure, and rutted up fields at harvest.
● Early plantings of snap beans and sweet corn have variable and reduced stands due to seedling blights, crusting over with heavy rains, and standing water in fields.
● Hail and severe winds have affected several vegetable fields with significant damage.
● Quality of vegetable transplants this year has often be substandard due to having to hold plants too long in greenhouses, overcast and cloudy weather causing stretch, and diseases such as gummy stem blight attacking plants in humid greenhouses.
● Not only are plants in the field being subjected to extra disease pressure, but wet soils will have low levels of oxygen, causing deleterious physiological changes to vegetable and fruit plants. The following are excerpts from an article we posted in the WCU during the last wet season we had in 2003:
“When soils are water-saturated, plants roots can be in an oxygen-deficient condition and thus respiration and metabolic activities can be markedly impacted due to low oxygen and high levels of carbon dioxide and other chemicals. Therefore, most of the functions normally performed by the root system are in potential jeopardy of performing poorly or in altered manners. The temperature at the time of the saturation and the duration of the events greatly impact the severity and symptom pattern.
“Saturated soils result in loss or reduction in normal root functions. Nutrient and water adsorption and their translocation are often impacted; consequently, wilting, yellowing, stunting, and nutrient deficiencies are the most common symptoms associated with flooded soils with most vegetables.
“During periods of high evaporation or high temperatures, the aboveground symptoms of saturated soils usually involve wilting and severe stunting, but the cool temperatures have limited such development this year. As temperatures start to increase, expect to see much more of the sudden wilting and yellowing of plants.
“Hormonal imbalances often occur when roots are in saturated soils, especially at cool temperatures, as production declines in the root-made hormones while stress/aging hormone production increases in other parts of the plant. These shifts create serious imbalances in the levels, ratios, and timing of hormones which results in abnormal plant development. Some plants are showing strong leaf epinasty (bending and twisting of the leaf petioles) resulting from increased ethylene production, while adventitious roots proliferate from the stem due to auxin imbalance. Timing of flower production and development can also be greatly impacted, which can significantly impact timing of fruit for critical market windows.”
(Taken from “Wet Soils Impacting Vegetable Crops” Written by William Nesmith, University of Kentucky and edited for Delaware)
● Extra watermelon acreage was planted this year (more watermelons are often planted the year after a good season such as 2008). Unfortunately, some of this acreage has gone into marginal ground that has remained overly wet. This sets up problems with water damage and increased disease risk.
● We are seeing heavy gummy stem blight pressure this year. In particular, one of the pollenizer varieties is being heavy hit. Plants have come out of greenhouses with gummy stem blight setting up the problem. Once in the field, the disease has spread to other plants with the wet weather.
● Crown sets in early plantings of melons are reduced due to poor weather (rain and cold) during pollination, affecting bee flights.
● Many vegetable crops are behind and harvest will start later than normal. Watermelons and cantaloupes are 10-20 days behind. Tomatoes and peppers are also behind by 10 days or more. Sweet corn will see smaller delays in harvest.