The finish line is in sight; in fact, some of you may be harvesting, others seeing tomatoes develop a blush. Each day brings a different set of tasks that require stamina, as the heat and humidity increase. The plants are getting tall, suckers are proliferating....critters may be sampling, diseases may be creeping in. Watering, tying, feeding, pruning, troubleshooting - it can all get overwhelming. Ripe tomatoes are just around the corner, however...stick with it, stay disciplined and enthusiastic, and most (rarely ever all!) things will work out.
I know all of this not only from experience, but from comments on my Facebook page, from chats with gardening friends, and from emails sharing pictures, issues, and requests for help with diagnosis of this or that issue.
Following are some of the main things to watch for, and options for dealing with them.
Spotting and/or discoloration on foliage, particularly low on the plant or on the side away from the direct sun. See the three pictures below - early blight on two plants, and septoria leaf spot (three pics, left to right)
Early blight and Septoria are two fungal enemies of tomato plants that attack lower, inner and rear foliage that tends to get splashed with soil, stays wet and doesn't receive as much direct sun. Signs of this are spotting and yellowing or browning of foliage, and occasionally, stem lesions. Daily removal of any foliage showing spotting and discoloration, mulching to ensure soil doesn't splash up onto leaves, adequate spacing to allow air flow and sun exposure, and watering at the base of the plant are all important for minimization of the disease(s). Use of fungicides such as copper spray can be effective, but will help prevent infection of upper foliage, not fix the problems already there (hence it is important to remove and destroy impacted leaves). This is typically not fatal to the plants, but you have to keep on top of things. Warm, humid nights will lead to significant spread of the disease; seasons with lots of late day rain, meaning wet foliage overnight, will bring on significant infection.
Twisting or curled upper foliage
This is not a frequent issue for me and I don't have a good picture to share from my garden. There are three possible candidates for deformed, slender, twisted upper foliage; drift of herbicides from neighboring gardens, infection carried by cucumber beetles which lead to cucumber mosaic virus, or significant populations of aphids or white flies. Plants can often grow out of slight herbicide issues; be sure to look at the condition of newly emerging foliage. Cucumber mosaic or tobacco mosaic virus infection will permanently stunt plants - new growth will continue to be abnormal, and such plants should be removed. If the issue is a severe aphid or white fly attack, the presence of the insects on the reverse side of the foliage will be evident; remove the portion of the plant with the infestation; new growth will be fine.
Plants wilting, even when green and well watered
See the two pics below - both show mid day wilting - plants are well watered and show no discoloration
A plant that wilts in the hot part of the day even when well watered is typically bad news. If the foliage remains green, it is likely the beginnings of a vascular fungal infection such as Verticillium or Fusarium wilt (transmitted through the roots; typically the wilted stems will show markings or yellowing if this is the case). More serious is bacterial wilt, in which the wilted stems will darken to brown or black. In all cases, it is best to remove the plant and rotate away from that area of the garden.
Dark blossom ends on small developing fruit
The tomato plants are working hard at this time of year, continuing to grow, producing flowers, setting fruit and enlarging the tomatoes that set from the blossoms. Stress will cause a calcium deficit in the developing fruit, resulting in the dark blossom end spot that enlarges and ruins the tomato; this is called a physiological issue brought on by unfavorable conditions, not a genetic problem with the variety or seed. Mulching to ensure even moisture for the plant and providing enough water to minimize mid day wilting will help minimize blossom end rot. Often the first few fruits on a plant will develop the rot, and certain shapes, such as paste tomato types, are more prone. As long as you have an adequate supply of calcium in the soil and a pH that is suitable for tomatoes, the problem should ease as new tomatoes set on the plant. Container grown plants, due to the finite water reservoir and possibility of mid day wilting when really hot, are most prone.
Tall, healthy plants with only a few tomatoes coming along
Tomato varieties are like us - each has its own personality and preferences. The really large fruited heirlooms are fussy when it comes to temperatures and humidity that make them happiest. High heat - over 90 degrees - and humidity during flowering will lead to an inability for the flowers to pollinate, and they dry up and drop off. Eventually, flowering should happen when the conditions are more suitable for the given variety. Smaller fruited tomatoes are less fussy and suffer less blossom drop.
Plants reaching the top of the stakes
Gardeners who stake their indeterminate tomatoes have two choices - let them just keep growing, wave in the breeze, and eventually bend over and droop downward....or top them when each fruiting stem reaches the top of the support stake. This takes discipline, because topping stems means removing future flowering and fruiting potential. Often, the overgrown stems will kink and possibly break - and often the flowers on the over-long stems won't have time to fully ripen the resulting tomatoes before frost. This year I vow to be a more disciplined plant topper! I have some useful videos on topping on my resources page.
I hope you found the above helpful as a brief trouble shooting guide to the most prevalent tomato problems, as least in my experience. Keep asking those questions!