Fixing Tomato Plant Problems: Handling Pest & Growth Issues

Heather de Paulo
Nov 15
4 min read

While this Herb Talk is about problems and pests you may see with your tomatoes, you could see them with other plants, as well.

Heather complains quite often that she has trouble with pests and disease on her tomatoes. The plants seem to be doing great, flowers are blooming and even little tomatoes start forming when suddenly, the leaves start curling, the plant turns yellow and the flowers and tomatoes start falling off! 😨

Now that she tried to plant tomatoes again (in pots, iguanas tend to eat everything she puts in the ground where she lives!), she is asking for my help along the way. She sent me some photos, so I thought I would share her problems, hoping it may help some of you.

Are Your Tomatoes Too Crowded? Let's Fix That!

The first thing I noticed was that she had several tomato plants in one pot, in some cases less than a gallon-sized pot.

congested plants in a pot tomato plants problems — Too many plants in a small pot

Tomato plants become large and develop a large root system. There should be one plant per pot. If you are going to keep it in a pot, consider a 3-gallon pot.

You will probably need to fertilize more than when they are in the ground. When they are in the ground, the roots will seek nutrients and moisture. When they are in a pot, you have to supply those needed nutrients and regulate the moisture on a regular basis.

Rain, Rain, Go Away—Or At Least, Don't Wash the Nutrients Away!

When you have a period of lots of rain you will have to replace nutrients washed out from the higher amount of water. A few inches of rain will not be an issue, but a couple of weeks ago, we had a week that totaled 5-6 inches of rain, which would definitely push the nutrients through and out of the pot.

When you are having dry periods, you need to watch for moisture. Even though the top appears moist, it might not go to the bottom. This is where a moisture meter comes in handy.

A moisture meter in a plant pot — Moisture meter

Once the center or bottom is too dry, the media doesn’t always absorb throughout the pot to remoisten the whole pot. In this case, I tend to set the pot in something so the water wicks up through the bottom. However, I don’t leave it like that unless I am monitoring. Your regular watering over time would keep the tray wet, thus causing too much wetness which will kill the roots.

Pots have holes for drainage, so as long you see it draining you should not have to worry about the plants staying too wet.

Are Your Tomato Leaves Turning Yellow? Here's Why

Besides being in pots that were too small, some of Heather’s plants were chlorotic (yellow) and not robust, not happy full leaves. Some had spindly leaves, this could be the variety, but because of the yellowing, I thought there’s possibly a nutrient problem.

I asked when she fertilized last and what she was using. She said she hadn’t fertilized since she had purchased the plants (busy, busy, busy)! It happens, but that explains the look of the plants. When she fertilizes, she uses organic products, like the fish emulsion I mentioned in a prior Herb Talk.

Could It Be a Fungus? Here’s What to Look For

I also noticed what might be a fungal problem. I would normally take my 10X lens and see if I notice if the leaves have a fuzziness that might indicate a fungus, which is spread by spores in the wind or rain. When the spores land on the leaf, they germinate and grow. To discourage germination, the leaf needs to be coated with something to discourage spore growth. There are many commercial options, but if you have fungus remember it is not a bug, so that is not your target. For those who are interested I have included a link that discusses using milk.

How to Use Milk Spray to Control Powdery Mildew

Remember when a plant becomes weak for any reason, it promotes problems, whether disease or pests.

Tiny Tunnels in Your Leaves? That’s a Leaf Miner!

Heather also saw there was leaf miner, which is a tiny fly that lays its larva within the leaf tissue. The larvae eat within the leaf making a tunnel until it matures, then hatches out to start the cycle again.

Leaf miner looks like a white vein in the leaf

Sometimes if you are watching this tunneling you can see the larvae within the tunnel. I just squeeze where I see the larvae, it is tiny, it won’t be gross. If you don’t want to squeeze and it is a small area on the leaf, just remove the area of the leaf or remove the whole leaf. If you stay on top of it, it helps to keep the problem to a minimum.

Systemic Pesticides: The Last Resort

Since the pest is between the leaf tissue, using a systemic insecticide is the only way I know to really control this if it gets out of control. BUT systemic pesticides are not considered a soft insecticide.

You have to consider when the plants flower and how long the chemical stays in the plant's system. There are sources that let you know how long these chemicals stay in these different crops. They are detrimental to pollinators. So, staying on top of scouting and addressing these pests before they get out of control is important.

Stay One Step Ahead of Pests!

If the populations get out of hand, systemics are the only option I am aware of. The leaf miners do not damage the fruit, but they will damage enough foliage to weaken the plant which will affect the fruit in the long run.

When the populations become high with any pest, my experience is that each year the pest tends to increase their population, making it even more challenging to control, so stay on top of your plants!