Extension agent: Protecting tomatoes in warm, wet weather
Published 12:00 am Friday, June 26, 2015
This year some of our tomatoes are running a little behind due to the cooler spring temperatures and rainfall. We’re seeing a lot of vegetative growth at the expense of flowering.
Usually this is due to over fertilizing with water soluble liquid fertilizer. Many of these fertilizers are high in nitrogen which stimulates the vegetative growth. Bob Westerfield, UGA extension specialist, recommends halving the ratio that is recommended on the container.
Wet weather also stimulates diseases. The best bet against diseases is to select resistant varieties but diseases can still be a problem. When examining plants for disease problems, the lower leaves will usually show symptoms first.
Warm, wet weather is usually indicative of disease problems in tomatoes. Septoria leaf spot and early blight usually attack the lower leaves first and both may be present at the same time.
Septoria first appears as small, water-soaked spots that become circular spots about 1/8-inch in diameter. It progresses to grayish white centers. Tiny, black specks may appear at the center. These are the fruiting fungal bodies. Spores may be spread by splashing rain. The lower leaves turn yellow, whither and fall off.
Early blight’s most obvious symptom is the premature loss of the lower leaves. Brown to black spots ¼-inch to ½-inch with dark edges appears on the lower leaves. The spots merge forming a “target” appearance. The fungus may also attack the stem end of the fruit causing concentric rings and black, velvety appearance.
Pick off these contaminated leaves and hopefully this will curtail the spread of the fungus. Make sure you have plenty of airflow as well. This keeps the leaves dry and hinders the fungus growth.
Another common problem is blossom end rot. The bottom of the fruit starts to decay. This looks like a small darkened or water soaked area around the blossom end of the fruit. Usually it becomes inedible plus it’s very unsightly.
It’s caused by a lack of calcium in the fruit. You can have plenty of calcium in the soil and the correct pH and it will still happen. It happens more often when the pH and the calcium level are low. Calcium in the soil is dissolved and transported up through the plant.
Most of us tend to over fertilize tomatoes with nitrogen. This spurs rapid growth in the leaves and the vegetative part of the plant. When it gets hot and dry, water will be transported to the leaves first. This is where most of the calcium will end up instead of the fruit.
Most of this water will be lost to transpiration as the plant strives to stay cool. Blossom end rot usually shows up in the first cluster of fruit. When fertilizing tomatoes, limit the nitrogen by using a 5 – 10 – 10 fertilizer ratio. Ratios such as a 10 – 10 – 10 or 13 – 13 – 13 may cause problems. The first number is the percent nitrogen in the fertilizer.
Using the spray on liquid calcium products usually don’t work because by the time the fruit is set, it’s very difficult to get the calcium through the skin of the tomato, which is much thicker than the leaves. Ninety percent of the calcium that the fruit requires should be there by the time the tomato is the size of your thumbnail.
As the tomato matures, the bottom shrinks due to the lack of calcium. Now some of the calcium that you spray on may end up in the soil and absorbed by the roots and moved up to the new fruit sets.
You can mix your own calcium chloride – 95 percent calcium chloride – solutions at a rate of four level tablespoons per gallon of water. Apply every seven to 10 days until you have made three or four applications. This will salvage your remaining crop.
Other preventive measures are to soil test. Then lime and fertilize to test recommendations. The pH needs to be between 6.0 and 6.5. Mix the lime and fertilizer into the root zone prior to transplanting the tomatoes.
Some problems such as leaf curl are caused by fluctuations in moisture condition. The tomato plant goes from very wet conditions to very dry conditions. Even out the moisture swings. Mulch the plants with pine straw, pine bark, compost or newspapers to maintain an even soil moisture.
Do not let the plant become water stressed, but don’t over water. Tomatoes need 1.0 to 1.5 inches of water per week. Avoid hoeing that may dry out the soil near the plant as well. If necessary, hoe shallow.
Be aware that black plastic mulch may cause overheating of the tomatoes as well. The point is not to cause extreme fluctuations in soil moisture that may cause Blossom End Rot.
What’s going on in Extension?
Market on Main: Every Saturday Morning from 8 a.m. to 10 p.m. The freshest produce in Troup County.
July 13-17: Up Camp with 4-H. Come get two thumbs up by growing up, dressing up and acting up with Troup County 4-H. Lots of fun activities. Ninth through 12th graders; cost is $45.
July 20: Beekeepers, 7 p.m., Ag Center.
August 18: Troup County Cattleman. Forages and Nutrition; Dr. Kim Mullinex, guest speaker, 7 p.m. Tuesday. Program will start at 7:30 p.m. The $6 meal will be served at 7 p.m. Ag Center.
Market on Main begins Saturday mornings from 8 a.m. to 10 p.m. Come by and enjoy the pick of the day. Carmike Cinemas LaGrange 10 theater parking lot.
If you have any questions or concerns, stop by or call the office.