August 13, 2014
Whenever you get cooler nights and the dew settles on the plants, it is an ideal situation for the spread of fungus diseases on your plants. Whenever we get late in the day thunderstorms, the rain wets the foliage of plants and the wet foliage can cause the spread of fungus diseases. If you water your plants late in the day, the wet foliage can lead to the spread of fungus diseases. What all this means to you is that you should be checking your plants for signs of fungus diseases at this time of the season.
Over the past week, we have had a tremendous number of people who have come into the store with leaf samples that show signs of fungus diseases. Once the fungus disease has started on the plant, it is important to apply a fungicide to stop the spread of the disease. There are two types of fungicides. There are preventative fungicides and there are curative fungicides. Preventative fungicides are applied to plants before the diseases begin on your plants. Curative fungicides are applied before a disease starts and can be used after a disease starts to prevent the spread of a disease. Once a disease has started, a preventative fungicide generally won’t be effective at stopping a disease from spreading. If you have a disease on your plants at this time of the year, it is best to apply a curative type of fungicide to your plants.
In the last week, we have seen a lot of tomato plants that have developed leaf spot on the leaves. This fungus usually starts on the bottom leaves and progressively spreads to the rest of the plants. Cucumber and squash plants have developed a white discoloration that covers the leaves. If you first look at the leaf, you may think that there is powder on the leaves. This disease is called powdery mildew. All of these diseases should be immediately treated with a curative type of fungicide. You should spray the infected leaves and you should spray the uninfected leaves. This approach will help to prevent the spread of the disease. If you find any unusual type of discoloration of the leaves on your plants, take a sample of the leaf, put it into a clear plastic bag and bring the sample into the store. Please keep in mind that photos of the plant aren’t clear enough in detail to allow us to make a proper diagnosis.
Late last week, a customer came into the store with a tomato hornworm caterpillar that looked to be covered with grains of rice all along the back of the caterpillar. To those who don’t know what is going on, it is quite the sight. If you are eating while I explain the rest of this column, you may want to stop reading now and finish the column later! The tomato hornworm is a major pest on tomato plants. The caterpillar eats leaves and can strip many of the leaves off of your plant. If you have a few on your tomato plants, they can remove the vast majority of the leaves. Mother nature in her wisdom sends the Braconid wasp to help you to control this caterpillar. The wasp lays eggs on the caterpillar and the eggs hatch out inside the caterpillar. The larvae of the wasp feed on the muscle tissue of the caterpillar but not on the internal organs. This allows the larvae to have a continually living host to supply the larvae with food. At some point in time, the larvae exit the inside of the caterpillar and form cocoons on the outside of the caterpillar. The things that look like rice on the caterpillar are actually the cocoons. In time the cocoons will open and a new generation of Braconid wasps emerge to infect more tomato hornworms. Natural pest control. If you see a tomato hornworm on your tomato plant and the hornworm is covered with the white cocoons, just leave it alone. Soon enough the caterpillar will die after a new generation of wasps has hatched and gone looking for more tomato hornworms on your tomato plants.
Well, that’s all for this week. I’ll talk to you again next week.