Getting Into Gardening

Whiteflies

We have gotten plenty of rain lately and that is great, but now some folks around Hays County are reporting an increase of pests in the garden. Warm, wet conditions are going to promote an increase in some insects but do get too worried because as the pest populations increase the beneficial insect population increases, too.

That being said, however, pockets of destructive insects can cause loads of damage in home yards and gardens and even in farm fields. One of these bugs is the Whitefly. Much like aphids, whiteflies are a scourge in the garden. These tiny pale pests suck the sap from plants and spread diseases. Worse yet, they’re so miniscule that they can fit through some mesh screening. Because of this, the whitefly is also a major problem in greenhouses and indoor growing spaces.

What are whiteflies? These pesky things are unpleasant and unsightly tiny, white, flying insects that just love to infest gardens, vegetable patches and greenhouses. Whiteflies, also known as aleyrodidae, are soft-bodied, winged insects closely related to aphids and mealybugs. They can be found in most any region, but they are so tiny that they are usually camouflaged.

They can be as small as 1/12 of an inch, somewhat triangular in shape, and are often found in clusters on the undersides of leaves. They are active during the daytime, so they are easier to spot than some other nocturnal pests. Whiteflies are capable of overwintering and reproducing throughout the year in warmer climates.

One common species of whitefly is the silverleaf whitefly, which is slightly smaller and more yellow than other whiteflies. Silverleaf whiteflies are especially common in southeastern states and it is most often the one we find in our gardens. You’ll often see whiteflies in mid- to late-summer when it gets warm; they are also a common pest in greenhouses. All species of whiteflies affect a wide variety of plants. Whiteflies tend to suck on ornamentals and warm-weather vegetable plants, including tomatoes, eggplant, peppers, and okra. They also like sweet potatoes and plants from the cabbage family.

Whiteflies go through four stages before reaching adulthood, and this takes a mere four weeks in summer and about six months in winter. Only the adults can fly, so a cloud of swarming whiteflies is a sure sign that you have a heavy infestation. Beneficial garden insects prey on the whitefly and provide some control in gardens not heavily sprayed with pesticides. Employ a range of manual and non-chemical control methods as the most effective treatment.

Although considered by virtually all experts to be more of a nuisance than anything else, large numbers of whiteflies can stress the plants they infest. The biggest problem is that their sap-sucking can transmit diseases. And their black, sooty “honeydew” can make a big mess.

In our part of the country, where we don’t get many freezes, these pests can become a perennial problem if you ignore the them. So, what do you do? Well, to start with, no more Miracle-Grow or other chemical fertilizers; the quick but weak growth you get from these wretched things attract these pests like mad. Better to build up your soil with lots of compost and other organic matter, get a nice non-wood-based mulch down, and invest in yellow sticky traps.

Whiteflies can’t resist the color yellow, and so most garden centers and catalogs sell packaged yellow sticky traps. These are great for all indoor situations, and even for a few potted plants outside. But if you need to protect large areas outdoors, you might want to make your own bigger ones. Paint sheets of plastic or cardboard bright lemon yellow and coat them with an “insect trapping adhesive” (sticky stuff), like ‘Tanglefoot’. Hang the traps around the affected plants and the adults will get stuck to them.

Now, you have to replace the traps when they become full of felons, so it’s best to try and knock the population down a bit first. One way is to have a helper disturb the plants while you suck the flying hordes into a canister vacuum or Shop-Vac. Don’t laugh; giant vacuums were being used for pest control on Texas farms just a few years after the home version was invented.

Or use a spray to reduce the population before you put your traps in place. Many gardeners tell me they’ve found sprays of all kinds to be ineffective against this pest, but that’s often because they’re spraying the wrong part of the plant. They’re hitting the part that they can see, the tops of the leaves. But whitefly adults and nymphs - and the next generation’s eggs - spend virtually all their time on the undersides of the plant’s leaves. So, spray that hidden area well with insecticidal soap or a light ‘summer spray’ (vegetable-based) horticultural oil; this will smother the eggs and nymphs, and maybe get some of the adults.

Now these creatures reproduce fast; the eggs hatch in just a few days and every time a bell rings, a whitefly nymph gets its wings (or a couple of weeks after it hatches, whichever comes first). That makes weekly sprays a good idea. You can also spray the plants preventatively next Spring with a garlic-based repellant or Neem oil.

My most successful efforts have been with insecticidal soap. I generally recommend that people buy packaged insecticidal soap instead of trying to make their own; there is often a very fine line between creating a helpful spray and an unfortunate herbicide when making your own homemade insecticidal soap. But the USDA researchers I have spoken with have come up with a ‘home remedy’ specifically for use against whiteflies.

Add one tablespoon of liquid dishwashing soap (the regular kind; not one of these awful anti-microbial things) to a cup of vegetable oil (peanut, corn, soybean, sunflower or safflower) and shake well. Don’t use this as your spray; it must be diluted! Mix two tablespoons of this ‘master solution’ into a cup of water, shake well and spray on those infested undersides.

Both nymphs and adults damage plants by sucking the juices from new growth causing stunted growth, leaf yellowing and reduced yields. Plants become weak and susceptible to disease. Like aphids, whiteflies secrete honeydew, so leaves maybe sticky or covered with a black sooty mold. They are also responsible for transmitting several plant viruses.