Mites don’t have wings, but they can spread through your crop almost as fast as flying insects or the airborne spores of fungi. There’s more on the spreading speed of mites further down.

Apart from a lack of wings, like other arachnids, such as spiders and ticks, they have an abdomen without segments (like insects have); it’s a flexible bag. Mites have their own special grouping called Acarina which divides again into chewing/mandibular mouthparts for mites that eat grain, books, straw, birds, people (as in scabies) ...or modified abrading and sucking mouthparts if they specialise in eating plants.

They need warm and moist situations in which to live. Especially those with the chewing mouthparts that eat dry tucker; not that the mites found in stockfeed bins or even silos are doing it too tough, after all, if the equilibrium moisture content was not high enough, they wouldn’t have even started.

Mites that eat living plants get their moisture direct from plants. There are thousands of species; most have the ability to dine happily on more than one type of plant… meaning what you are growing as well as surrounding vegetation.

Newly hatched spiderlings often disperse by letting out a few centimetres of web filament and, when it catches a breeze, they let go of where they are standing and float off until they arrive somewhere. Methinks mites might also let out a few millimetres of filament and float off until they alight on another tree. Being so small, a 0.4mm mite and 10mm of fine web is barely discernible. We also know webbing can and does provide a bridge between branches or plants.

It’s always informative in designing your control program to know where pests overwinter. If you grow deciduous trees, mites fall off with the autumn leaves and the ones that can endure winter are the last of the fertilised females, surviving if they are deep enough beneath the surface… preferably surrounded by leaf litter and other decaying vegetation.

Overwintering in soil is the modus operandi for most mite species. After emerging from the soil, they climb upwards. The first few new leaves are attacked and the next generation (less than two weeks later) move onto the remaining leaves. The next and subsequent generations, a week or so apart, means all the new leaves can become malformed as they open.

If you are in a tropical/subtropical climate, not growing deciduous crops, there are mites with a liking for tropical fruit. As is normal for most mites, they prefer the underside of the leaf. The lychee erinose mite, blisters the terminal buds preventing fruit set. That’s a fair way up from ground level and if lower-level branches show no signs of mites, birds and breezes carrying ‘hang-gliding’ mites get the blame for transfer. As mentioned, leaf deformation is normal, sometimes it is just discolouration and sometimes the plant distorts and grows unusual hairs. Often there is really fine webbing noticeable.

Spider mites, broad mites, russet mites, two-spotted mites and others are just variations on what we’ve covered. They are all very small; just a half to less than two millimetres long. Body shape can be ovoid to elongated (carrot shaped) depending on the species. To get up close and personal, you’ll need a mobile phone with a good camera (which might be more readily available than a 10X hand lens).

Just 10 or so eggs are laid daily, up to 200+ per female in her lifetime of say four weeks and those eggs produce predominately females at a ratio of maybe 3:1. Egg production also varies between species. The hatching larval form has only six legs. Within a day or so it has moulted into a nymph with eight legs and, after another few days and a couple of moults to allow an increase in size, they become randy males and females producing more eggs. Talk about a population explosion!

Control

Some suggest that mite populations quickly increase to become serious pests when an insecticide has been used against insect pests. I have another explanation: because mites are mostly on the underside of the leaf, they may not have been contacted; the insecticide probably would have killed them if you’d aimed it to hit them.

Another scenario: the insecticide not only killed the pest insect but also the predatory insects that do a great job of eating mites. There are little 2–3mm long black ladybirds, adults and larvae that can each eat a few mites per minute if they are on a good patch. Other ladybirds of the usual orange and black colouring and a bit bigger: 4mm and 6mm long, can eat even faster! And, while we are talking biological control, the companies that sell beneficials, also offer predatory mites. That type of civil war ought to be effective!

Most, but not all insecticides will kill mites. To find out for sure if what you spray kills both your insect pests as well as mites, just apply it to a single tree under attack by both mites and the pest and check in a few minutes. If they are both dead… go ahead. If not, you should change your droplet size, angle of nozzle or increase turbulence to get better contact onto the underside of the leaf. This testing process may take about 20-30 minutes but is well worth the time taken because the payoff continues. If your test found out you were getting close to 100% kill, by scaling back your application rate and re-assessing, you might easily find you are still getting the near 100% kill. You will not only save on the amount of solution per tree/hectare that you were using, but you also save worthwhile money each year.

Here’s to bumper crops and higher prices in 2022… due in part to your better understanding of how to remove the costs of pest damage from your calculations.

*Written by Ion Staunton an entomologist and owner of Pestech Australia – manufacturer of PyBo Natural Pyrethrum Insecticidal Concentrate. Any questions? Contact: ion@pestech.com.au 0407 308 867.