Cherry Tomato Problems: Splitting, Leaf Spot, Blight and Hornworms

Does it spread, or is it just this plant?

Every cherry tomato complaint falls into one of two boxes. Disorders come from uneven water or feeding, they stay on the plant that has them, and you have days to sort them out. Diseases and insects move down the row, and with blight in particular a delay of a week can cost you every plant you have. Working out which box you are in is always the first move.

Split skins, black bases and flowers that drop without setting are disorders. Spreading spots that grow rings, a plant that wilts and never recovers, and leaves being eaten overnight are the other category. Cherry tomatoes are hit harder by splitting than any other tomato and are somewhat more forgiving of everything else.

Splitting is the cherry tomato's signature problem

Thin skin and small fruit make cherry tomatoes far more prone to splitting than any large-fruited type, and a single night of heavy rain onto dry soil can split most of what is at full color on a plant. You will see either fine concentric rings around the shoulders, which come from slow moisture change, or a single deep radial split from the calyx, which comes from a sudden one.

Split fruit is safe to eat the day you pick it, so this is a loss of storage life rather than a total loss. Prevention is all about smoothing out the water supply: keep a mulch on, keep the soil consistently moist rather than swinging between dry and soaked, roof the row while fruit is coloring, and pick often enough that little sits at full color waiting for weather.

1. Pick everything colored before rain arrives Watch the forecast in picking season. An hour spent stripping the colored fruit ahead of a storm saves most of the crop.
2. Keep two inches of mulch on the root zone Straw or clippings stop the soil drying hard between waterings, which is what sets up the split when rain comes.
3. Use split fruit the same day It is fine to eat but it molds within a day and infects sound fruit in the same bowl. Keep it separate as you pick.

Leaf spot and early blight start at the bottom

Brown spots with faint concentric rings on the lowest leaves, often with a yellow halo, are early blight or one of the leaf spots. Spores live in the soil and get splashed up onto the lower leaves by rain, so it always begins at the base of the plant and works upwards. Left alone it defoliates the plant from the bottom, and a cherry tomato without lower leaves in midsummer will not fill its remaining trusses.

It is manageable rather than fatal. Remove affected leaves as soon as you spot them, keep two inches of mulch on the soil so nothing splashes up, and strip the lower leaves below the truss you are currently picking to let air through the base. Never water over the top of the foliage. If it keeps climbing, a fungicide labeled for tomatoes where you live will hold it.

1. Check the lowest leaves weekly While you do the suckers, look at the bottom foot of the plant, undersides included. Spots the size of a pencil eraser with rings inside them are the sign.
2. Remove and bag, do not drop Snap affected leaves off at the base and carry them off the plot. Dropped on the bed they simply reinfect from below.
3. Mulch as a barrier The mulch is doing two jobs: evening out moisture and physically stopping rain splashing soil-borne spores onto the leaves.

Late blight moves in days, not weeks

Late blight is the one that ends the season. It shows as gray-green, water-soaked patches on leaves that go brown and papery within a day, often with a fine white bloom on the undersides in humid weather, and it puts hard brown marbled patches on the fruit. It arrives in cool, wet, still spells and can take a plant from healthy to dead in under a week.

There is no cure once it is into the stems. If you catch it on a few leaves, remove them immediately, bag them, and improve airflow. If it has reached the main stem, pull the plant and get it right off the plot. Pick and use any sound fruit at once, because blighted fruit rots in storage and will not ripen. Do not compost the plants and do not plant tomatoes or potatoes in that ground next season.

1. Inspect daily in cool, wet, still weather Those are the conditions it needs. In a dry summer you may never see it at all.
2. Cut out early lesions the same day Remove the affected leaf and the one either side of it, bag them, and wipe your pruners before touching another plant.
3. Pull a plant with stem lesions Brown patches on the main stem mean it is finished. Take it out whole and remove it from the plot to protect the neighbors.

Airflow is the best defense you have. Two-stem training with 30 inches (75 cm) between plants, lower leaves stripped, and a roof over the row keeps the canopy dry enough that blight struggles to get started.

Hornworms, aphids and fruit flies

A cherry tomato stripped of whole leaves and small stems overnight, with dark pellets of frass on the leaves below, has hornworms. They are large green caterpillars that match the stem color perfectly and are almost impossible to see until you look for the frass and then work directly upwards from it. One caterpillar can strip a stem in two nights, and hand-picking is entirely effective.

Aphids cluster on the growing tips and whitefly sit under the leaves. Neither kills a vigorous cherry tomato, but both spread virus, so keep the numbers low with a jet of water or by squashing them, and hang yellow sticky traps at plant height. The other visitor is fruit flies, which arrive because of split and rotting fruit left on the plant; the fix for those is simply to pick up the fallen fruit.

1. Follow the frass upwards Dark green-black pellets on a leaf mean a hornworm is directly above. Look along the stems at that height rather than scanning the whole plant.
2. Leave parasitised caterpillars alone A hornworm covered in small white rice-like cocoons has been parasitised by wasps. Leave it where it is; it has stopped feeding and it is producing more wasps for you.
3. Wash aphids off the tips weekly A firm jet of water on the growing tips knocks them off while numbers are small. Do it in the morning so the plant dries.
4. Clear fallen and split fruit Rotting fruit under the plants is what brings fruit flies and mold. Pick it up every time you harvest.

Flowers that drop without setting

Cherry tomatoes set fruit more reliably than any other tomato, so when the flowers drop off the truss without setting there is usually a clear cause. Sustained heat above 90F (32C) sterilizes the pollen; nights above 75F (24C) do the same. Too much nitrogen produces flowers that never set. Very still, humid air stops the pollen shaking loose at all.

Heat resolves itself and the plant will set again as soon as it cools, so do not pull anything. In the meantime, shade the row through the hottest part of the day, stop feeding nitrogen, and tap the stake sharply on a sunny mid-morning to shake the pollen loose. Record the dates it happened: over two or three seasons the pattern tells you whether to shade earlier next year.

1. Tap the stake mid-morning A sharp knock on the stake between mid-morning and midday releases pollen. It makes the most difference in still, humid weather.
2. Shade through the hottest hours Shade netting or a temporary screen through the afternoon keeps flower temperature under the threshold where pollen fails.
3. Skip nitrogen while flowers are dropping Feeding harder makes it worse. Switch to a high-potassium feed or miss a round entirely.