Clean garden, plants much less appealing to mites and whiteflies
QFor the past two years I have fought either spider mites or whiteflies on my tomato plants. I have tried home remedies and everything the nursery has recommended, including neem oil. They end up having to be sprayed or treated in some way every week and ultimately they succumb to these awful pests. Could you suggest something that would really keep them from destroying the tomato plants?
AWhiteflies and spider mites are difficult to control once their populations become established. The individual insects are tiny and tend to hide out on the underside of leaves, so they often go undetected until they’ve caused considerable damage. Dull-looking, stippled leaves that turn brown and eventually fall are often the first noticeable sign of a problem. The presence of fine webbing indicates spider mites.
Prevention and treatment of spider mites and whiteflies are similar so, for the sake of brevity, my advice covers both.
To tackle this problem, we need to look at prevention first. Both pests prefer to attack plants that are water-stressed, so regular irrigation is crucial. They also prefer dusty conditions, so if you have a drip system, you may want to occasionally water from an overhead sprinkler to wash dust from your plants. A strong jet of water directed at the underside of leaves can remove many insects as well.
Remove heavily infested plants and discard — forget composting them.
Also, remove any dead leaves and detritus from beneath the plants, since this provides a breeding ground for more mites and whiteflies.
Avoid using broad-spectrum insecticides because they are more likely to kill off beneficial predator insects than pests. Since whiteflies and spider mites like to hide on the underside of leaves, they are likely to remain untouched by sprays. In the insecticide-free garden, many varieties of predatory insects will descend upon these soft-bodied snacks like a horde of hungry teenagers.
One broad-spectrum insecticide, carbaryl, has been shown to stimulate spider mite reproduction in the lab. Other organophosphates and some pyrethroids can cause spider mite outbreaks, especially when they are applied in hot weather.
Reflective mulches can repel whiteflies without harming beneficial insects. Sticky traps are available, but their usefulness is limited. If you want to trap whiteflies, I recommend painting stir sticks (for paint) bright yellow, then coating them with petroleum jelly and sticking them into the ground near the affected plants.
The commercially available traps are coated with a very sticky substance that has an unfortunate tendency to adhere to nontarget species (bees, lizards, cats and children, for example).
QI am having issues with my calla lilies. I planted one in full sun and the other gets about five hours of sun per day. The only time they’ve bloomed is right after I bought them.
ACalla lilies like moist soil but tend to suffer from root rot and die if the soil is too soggy. If your lilies are green and healthy-looking, they may just need some fertilizer. Apply a balanced fertilizer at the start of growing season to give them a little boost. If they look crowded but healthy, they may also need to be divided in the fall.
Have questions? Email gardening@scng.com. For more master gardening resources, visit ucanr. edu/sites/RiversideMG for Riverside County; mgsb.ucanr.edu for San Bernardino County; celosangeles.ucanr.edu/ UC_Master_Gardener_ Program for Los Angeles County; and mgorange. ucanr.edu for Orange County.