Spots on tomatoes

By GARY PIERCE
Posted 7/1/22

Finally, tomatoes are beginning to get ripe. It seems like we have waited forever to get good tasting maters again. As we watch these little green tomatoes swell up, nothing can be worse than …

This item is available in full to subscribers.

Please log in to continue

Log in

Spots on tomatoes

Posted

Finally, tomatoes are beginning to get ripe. It seems like we have waited forever to get good tasting maters again. As we watch these little green tomatoes swell up, nothing can be worse than simultaneously watching brown spots appear. The No. 1 cause of a big brown spot is blossom end rot.

Blossom end rot is when a large tomato is developing and the end furthest from the stem starts to turn brown. As the affected fruit gets larger, so does the brown spot. As the fruit turns orange, the brown spot may take up half the fruit.

The simple cause for this situation is lack of calcium during fruit development (flowering). The lack of calcium may be widespread (not much in the soil) or it may be temporary (plant can’t take it up).

Widespread lack of calcium is usually connected to low pH levels of the soil. Adding lime raises the pH and adds calcium. This fixes the widespread problem, but the fix isn’t quick. If you add lime now, then you will see the brown spots start to go away about midsummer. This is better than never.

While lime (calcium carbonate) is the primary way to add calcium, gypsum can also be used. Gypsum or land plaster (calcium sulfate) adds lime without changing the pH. This product is used extensively on peanuts. The water from boiled eggs can also be used. If you are making deviled eggs, keep the water for the tomatoes.

Temporary calcium shortages happen when the plants are used to getting water, then they hit a dry spell. The flowers produced during the dry spell will have fruit with lossom end rot. This problem goes away when the plants get water and calcium is taken into the plant with the water. Temporary shortages can be minimized by using mulch and irrigating during dry spells.

Tomatoes grown in potting soil are more likely to have calcium issues if the potting soil is mostly peat moss. Add a half cup of lime or gypsum to each potted plant.

The boiled egg water also works well with potted plants. Small tomatoes, like cherry, rarely display blossom end rot because they mature so quickly.

The second big spot problem is anthracnose. This is a fungal plant infection that appears in wet warm weather. If your tomatoes experienced this issue, it was probably around mid to early June.

This disease looks more like several brown blotches or spots together. The spots also have a sunken look or feel. Since it hasn’t rained since early June, anthracnose is not on the latest tomatoes. During the dry weather, blossom end rot kicks in as the primary brown spot problem.

Rotating your tomato garden from year to year may help with an anthracnose problem. Spraying is seldom necessary.

You can eat tomatoes with anthracnose or blossom end rot. Do you really have to be told to cut off the brown area? Most folks just pull the tomatoes off whenever brown spots are discovered. Aren’t we all looking forward to sinking our teeth into some juicy spot-free tomatoes?

Gary Pierce is an agriculture teacher at Triton High School.

Comments

No comments on this story | Please log in to comment by clicking here
Please log in or register to add your comment