Knowing the origin of pests helps with proper control

Suzanne Wainwright-EvansNo matter what you do, they always seem to come back -- pests that want to feed on your crops. But where do they come from? Believe it or not, they do not spontaneously generate nor are they from bad Karma. In reality, they invade your crops in a few different ways. The most obvious is some pest insects simply arrive under their own power, flying or crawling in to feed on a vast monoculture feast that growers provide for them. Over the centuries, many pests have developed a keen ability to locate their host plants over great distances. Without this talent, their species would not be able to survive.
   
Another way pests can get around is by hitching rides. Immature scales hitch rides on bird feet, hoping the bird will land on a suitable host. Pests also can hitch rides on farm equipment like tractors or even clippers. Employees can vector around insects and mites on their hands or clothing. It is possible for workers to vector diseases on their tools or shoes. Other wingless pests, such as mites, can blow in on the wind. Even some of the winged insects that are not strong fliers (like aphids) can also ride the wind currents. Unfortunately one of the ways pests make it to your growing facility is in a FedEx box, or a pallet of liner stock. To add insult to injury, you have actually paid for the delivery.

Scout, scout, scout
Sometime pests can show up, or you think they just showed up, when in truth they may have been there all along, just in low numbers. When the pests have the right host and right environmental conditions, their numbers can explode quickly, often appearing to have arrived overnight. This is why scouting is so important and catching the pests before their numbers get high.
   
Pests can hitch a ride on people, plants, tools and equipment.Often people take a quick glance at arriving plant material, not taking the time to carefully inspect it. I often hear from growers that there is just simply no time to inspect the newly arrived material. These new arrivals need to be inspected from roots to leaf tips because small pest problems can become troublesome problems fast. It is a lot easier and cheaper to treat a few plants upfront then letting the plants become Typhoid Mary to your production facility.
   
Before starting your inspection, make sure you know which variety of plant you are looking at, and what the most common potential pests may be. This will include insects, mites and disease problems. It would be helpful to keep a running list of problems you have found in the past, making this available to the employee doing the inspecting. Be sure to include details about the plant variety, specific vendors and delivery dates. This information will help you watch for potential issues when inspecting cuttings or stock material that may have had some issues in the past. Keep a 10x hand lens handy to check for small pests that can’t be seen with the naked eye. Adequate lighting is also very important, because these pests can be very small, and light will make it easier to find them.

(Top) Whitefly eggs can be very small and easy to miss unless you are using a hand lense to scout for them. (Bottom) Spider mite eggs can be easily missed because of their size and transparent color.What to look for
Aphids – They can often be seen with the naked eye, but are more easily seen with a hand lens. They are often green so they can blend in with green plant tissue. Remember they do not have to mate to produce offspring, so all it takes is just one, and you can quickly have a high population. Don’t forget to check the roots because there are species of aphids that live on root systems.
   
Thrips – Often missed because of their small size, adult western flower thrips are less then 2 mm long, making hand lenses an absolute necessity. Eggs, which can’t be seen with the naked eye, can be laid on different parts of the leaf depending on the host plant. Keep in mind that some species of thrips pupate in the soil, so even if you inspect the foliage, that does not mean they are not present in the growing medium.
   
Whitefly – Adults are easily seen flying around plants, but the immatures (or crawlers) are the size of a pin head and can be difficult to locate. Whitefly eggs are small -- about 0.2 mm. After hatching, they attach themselves to the plant tissue and feed before going into the pupal stage. Pupae resemble a scale insect but are about 0.7 mm. There are mostly found on the underside of the leaves.
   
Scale and mealybugs – Adults are often easily seen because of their size, but the crawler stage is often missed because of their light color and small size (less than 0.25 mm). Root inspection is necessary because there are species of mealybugs that live on the root systems and can be difficult to control once established in your operation.
   
Spider mites – With a trained eye, species like two-spotted spider mite adults can be seen with the naked eye, but a 10x-30x hand lens is necessary to find eggs. Finding the eggs is so important because often many growers spray miticides that just kill the adults and not the eggs. If a pesticide spray had been applied, the adults could have been killed but the eggs will survive. What might look clean may be a ticking time bomb. Once they hatch, their numbers can explode if conditions are right and they can quickly get out of control.
   
Fungus gnats – Adults are easy to spot. They look like miniature (around 2 mm long) mosquitoes. They do not often travel in plant cuttings, but more likely on rooted material with growing medium (like liner material or plugs). It is important to pull random plugs out of the trays and inspect the roots for cream-colored fungus gnat larvae. If found, treat with beneficial nematodes. Fungus gnats can vector plant diseases, so these are not something you would want to bring into your operation.
   
Taking time to carefully inspect all plants arriving at your operation and treating the problem will save time and money in the long run. Don’t be afraid to contact plant suppliers if there is an issue with arriving material, because they may not be aware of it.