No Joke: Tomatoes are Cracking Up

Photo: Debbie Roos

Tomatoes are cracking up after the recent rains, but growers are not amused. Recently, we’ve seen in an increase in the amount of tomato surface cracking. Tomato cracking is an abiotic disorder of tomato fruits that is associated with growing conditions. When tomatoes are left on the vine too long or during periods of rapid fruit growth, the tomato epidermis (or skin) does not have enough elasticity to compensate for the sudden growth. Eventually the skin splits and bursts.

There are two main types of growth cracks 1) radial cracking, which is splitting of the skin from the stem scar towards the blossom end and 2) concentric cracking, which is splitting of the skin in a circular pattern around the stem. Radial cracks occur during humid, hot weather. Concentric cracks occur during rapid fruit growth associated with rainy weather following a period of dry weather. The earlier growth cracks occur during fruit development, the more damaging they are. Growth cracks can provide the perfect entry point for secondary fruit rotting organisms.

Photo: Debbie Roos

The most important means of controlling growth cracking is maintaining a steady, adequate supply of water or irrigation flow, especially during hot, dry conditions. Avoid over and under irrigating. Mulching also will help prevent dramatic fluctuations in soil moisture. Be especially wary if weather was cool and overcast followed by sunny, hot, and dry periods, and then high humidity and rainfall. Keeping foliage healthy and disease free is also critical. If the fruit lacks leaf cover, cracking can be more of a problem. Remove mature fruit right after heavy rains to prevent cracking. Follow recommendations from Cooperative Extension about plant nutrition, because high nitrogen and low levels of potassium can contribute to fruit cracking. Some varieties are more prone to cracking and can show cracking when the fruit are still green. Even varieties that show some resistance to cracking in the green stage may crack once the fruit starts turning red. Plum varieties like ‘Heinz’ and ‘Marglobe’ crack less than cherries and the larger fruited varieties like “Better Boy.” If you have a history of tomato cracking in your tomatoes, you may try switching to one of these varieties, ‘Daybreak’, ‘Jet Star’, ‘Pink Girl’, ‘Monte Carlo’, ‘Mountain Fresh’, ‘Mountain Spring’, and ‘Spitfire.’ New varieties are released regularly, so check with your local cooperative extension agent for latest variety recommendations for tomatoes.

by: Emma Lookabaugh, Chris Gunter, and Barbara Shew

Sample of the Week: Tomato Triple Whammy

Tomato Sample, notice the puckered leaves (Photo: E. Lookabaugh)

This week’s Sample of the Week came packing a triple threat! A client brought in two tomato plants from their greenhouse. As soon as we opened the bag, a cloud of whiteflies flew out, alerting us to culprit number 1. Whiteflies damage the foliage when they feed, resulting in yellowing and curling of the leaves. In heavy infestations, whiteflies can cause stunting of the plant, reduced vigor, and leaf drop. Prevention is the best management option for whiteflies. All incoming plants should be checked before they are introduced into the greenhouse. Once the whiteflies are established in the greenhouse, you can starve them out by removing all host plants for at least two weeks, or a more practical option is the use of sticky traps. Whiteflies are attracted to bright colors like yellow and white so hanging white or yellow sticky traps above susceptible plants can reduce population numbers. 

Whitefly damage, look closely and you can see the whiteflies (Photo: E. Lookabaugh)

Upon examining the foliage, we noticed the leaves seemed stunted and distorted. Some of the leaves appeared puckered. We also saw light green etching or mottling on some of the foliage. Distorted foliage in combination with stunted new growth and mosaic or mottling of the leaves usually points toward a virus infection. We ran assays for the common viruses associated with greenhouse tomatoes and determined Tobacco Mosaic Virus (TMV) was culprit number 2. TMV is a serious threat to greenhouse plants. It is spread through contact with tools, workers’ hands, or infected plants. Pruning, tying, and transplanting are great ways to accidentally spread TMV to healthy plants in the greenhouse. TMV has a very wide host range and can survive on root and plant debris for long periods of time. Virus particles can also survive in cigarettes or chewing tobacco so workers who smoke or dip should wear gloves when handling TMV-susceptible plants. Strict prevention and sanitation programs provide the only means of controlling the disease. Use disease-resistant varieties and disease free seed/ transplants whenever possible. Encourage workers to dip hands in milk, wear gloves, or wash hands with soap and water before and after handling plants. Do not touch healthy plants after handling infected plants. Remove any nearby weeds that could harbor the virus. Infected plants and plant debris should be removed immediately. 

TMV Symptoms (Photo: E. Lookabaugh)

TMV Symptoms (Photo: E. Lookabaugh)

Finally, we checked the roots to provide a complete diagnosis. Amazingly, we noticed swollen and knotted roots caused by root knot nematodes, culprit number 3! Above ground, root-knot nematodes can cause yellowing, stunting, and wilting. Usually root-knot nematodes are not a problem in greenhouse tomatoes and other plants grown in treated potting mixes. These particular plants were being used in a research study so they were being grown in soil intentionally infested with nematodes. 

Root knot nematode, notice the galls on the roots (Photo: E. Lookabaugh)

Unfortunately, these tomato plants probably won’t make it. Whiteflies, TMV, and root knot nematodes can pack a serious punch to tomato plants individually-- imagine having all three!

For more information, see links below:
http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/vg15.htm
http://www.ipm.ucdavis.edu/PMG/r783301211.html

Herbicide Injury to Tomatoes

"Classic" Glyphosate Symptom

Recently, the clinic has received several tomato plants with symptoms of herbicide damage. Glyphosate (found in products like Roundup) causes very distinctive yellowing symptoms at the base of tomato leaflets.  Broad-leaf weed killers (2,4-D type herbicides) cause stunted and deformed new growth, and whipping and curling of the leaves.  

2-4 D Type Injury 

Tomatoes are very sensitive to herbicide injury and damage can be severe.  In extreme cases, simply touching tomato plants with herbicide-contaminated hands or clothing can cause injury. 

Spray drift is an important source of herbicide damage. Sometimes symptoms appear in a gradient pattern, with plants closest to source being more affected than those further away. 

Be careful to prevent herbicide drift into home gardens, farms, or greenhouses where tomatoes are growing. To reduce the chances of spray drift, do not apply herbicides near these areas on windy days.  

Glyphosate Drift in Greenhouse

Some herbicides are formulated to provide season-long protection against weeds. Planting sensitive crops too soon after using one of these herbicides can cause injury. Check the product label to see when it is safe to replant following herbicide application.

Glyphosate Injury

Sometimes farmers and home gardeners report problems in vegetables and flowers after applying hay, manure, grass clippings, compost, or other amendments to soil.   Symptoms include poor seed germination, twisted, cupped, and elongated leaves, and misshapen fruit. Young plants may die and yields may be reduced in mature plants.  This damage can be traced to herbicide carryover in the soil amendment.  For more information on herbicide carryover in soil amendments, click here.