Tomatoes

A couple of high tunnels and even a field of tomatoes have been found with tomato spotted wilt virus in Maryland. The high tunnel finds were not too suprising but the field was a bit as we usually do not see field infections until later in the season.

Southern blight is a fungal disease that is most common in the tropics and subtropics, but also is found in the SE United States in the summer. In Maryland we usually find it in the southern part of the state in counties like St. Mary’s, Charles and Wicomico. It has been found this year in more northern counties such as Frederick, Montgomery and Baltimore.

This has been a very wet period for most of us in the mid-Atlantic. Some fields have received repeated downpours of rain and have standing water while others have not gotten as much. But in almost all of the tomato fields I have found rain check (fig 1).

Tissue tests taken in tomato fields over the last 6 weeks show that fields with good levels of potassium (K) (>3.2%) have overall lower levels of fruit ripening problems than fields with below recommended levels of K (< 2.5%). Figure 1 shows an example of a tomato with good levels of K, while figures 2 and 3 show what often happens when K levels are too low.

Physiological Tomato Fruit Disorders

Nutrient Problems and Their Management in Tomatoes

The high temperatures we have had this week and probably next week with daytime highs at 90oF and above and nighttime lows only getting down to 70oF in much of the mid-Atlantic may cause blossom drop and fruit abortion in tomatoes. Ordinarily in tomato fields pollination is achieved just by the action of the wind. Pollen is released from the tomato flower and falls onto the stigma.

Tomatoes are grafted by joining the top of one plant (the scion) to the root system of another (the rootstock). The subsequent plant is more vigorous and productive. Several studies have been done over the last 10 years that show the benefits of using grafting for soil disease control in tomato production, but there is not much research that examines the influence of rootstocks when there is no disease in a tomato high tunnel production system.

As this growing season winds down and for the next few weeks it is a good time to examine vegetable roots for root knot nematode (RKN). I would be suspicious of having RKN if my vegetables seemed to need more water than normal or wilted during the heat of the day and recovered later or plants had nutrient deficiency symptoms rarely seen in your fields and the addition of fertilizers did not seem to alleviate the deficiency symptoms.

This heat wave we have had this past week will have repercussions over the next few weeks as the flowers of several crops including cucurbits, peppers and especially tomato will not pollinate or fertilize properly to develop into fruit. Daytime highs of 90o F and above and nighttime lows only getting down to 70o F in much of the midAtlantic for the last week will cause blossom drop and fruit abortion in tomatoes.