Achieving Good Insect and Disease Control

With what I experienced this past season, we want to discuss controlling insects and disease.  Outstanding control is the culmination of several management decisions.  Obviously, the chemistry choice for control (pesticides and/or biocontrol materials) is of the utmost importance, but your decisions do not end there.

You should also consider how your control product works; is it a systematic that moves through most of the plant, a translaminar, which moves only a short distance inside the plant, or simply a contact.  If a contact, read your label to determine the amount of time the chemistry is active, as a follow-up application will almost certainly be necessary.  Regardless, in all instances, to achieve good control your spray solution must cover most or all of the plant surfaces.

This was a lesson that I learned the hard way this past season when using SiMag 58 and SiGuard as part of my foliar nutrient sprays to help control my extreme aphid pressure.  Although I was pleased with the general level of control, it was also apparent that I still had rather high aphid populations.  Although it seems obvious now, it took me a little while to realize that I was not really spraying the parts of the plant where aphids were at, which of course was the underside of the leaves.  Once I realized this, I lowered my spray wand and began spraying more from an upward angle rather than from the top and simply letting the spray drift downward on the plant, which is common when applying foliar nutrient.  This allowed my spray to hit more of the underside of the leaves, and I did see a noticeable increase in aphid and mite control.

Also of consideration is water quality and how your pesticide will react with your water.  It is usually recommended to adjust either water pH or hardness to achieve optimum chemical performance.  Torch is an excellent choice for achieving optimum water quality.

The next aspect to consider is the equipment that you’re going to use for application.  In most instances a fine mist is preferable to larger droplet sizes, but always read your pesticide label as there are some that work better if the droplet size is somewhat larger, if for no other reason than to reduce potential drift.  The pressure, or force of the spray is also important in ensuring good plant surface coverage.  As I realized all too clearly, many of our insect pests such as aphids, thrips and mites are usually on the bottom of the leaves, or in other hard to reach areas.  If using a contact insecticide, or silicon for plant protection, it is necessary to get these materials where the insects are actually at.

Generally speaking it’s necessary to have at least 95 pounds per square inch of spray pressure, and over 100 is better.  This level of spray pressure is adequate enough to actually move the plant leaves around as you’re spraying, allowing coverage of all areas of the leaf, and inside the leaf canopy.  Many of our plant diseases initiate in areas of the plant where air flow is poor and the humidity is somewhat higher then on the outside areas of the plant.  Other diseases will often initiate at the lower levels of the plant from soil and rain splash, example being Septoria Leaf Spot, and then move upward resulting in significant leaf loss.

Airblast sprayers that cover many rows in a single pass and boom sprayers that direct pesticides downward seldom provide the coverage necessary for trellised tomatoes and staked peppers due to the density of leaves that need to be penetrated.  Spray equipment that only applies to the top of plants such as over the row top boom sprayers can be a major factor in allowing pests to get a strong foothold.  Even high pressure with lots of water to disperse the active ingredient often leaves major areas of the plant unprotected.  Airblast sprays always look like they are doing this amazing job of plant coverage and are often rated as covering fifty feet or more.  While effective for vine crops and tree fruit, or if you’re spraying every row, you should still realize that applications made from a spray aisle often leave substantial areas of the plant uncovered on plants in between these spray aisles.

Custom sprayer at the Penn State SE Research Farm, illustrating spraying from multiple angles.

You can check your level of coverage with water sensitive paper strips scattered throughout the plant canopy.  Fill your current sprayer with plain water, install the strips throughout the canopy, make a normal application and look for the color changes.  These strips are commonly available from agriculture spray equipment suppliers, and the results can be surprising: vine crop growers often discover that they need to slow down, increase pressure, or use more water; or all three.  Tomato growers often discover why defoliating diseases such as Septoria Leaf Blight and Early Blight always get away from them.

The ideal solution for outside staked tomatoes and peppers is a drip nozzle sprayer.  By spraying directly into the canopy from the side and top while using adequate water and pressure, it is much easier to get excellent coverage.  The shows a custom rig at the Penn State University SE Research Farm that sprays a single row with multiple spray nozzles.  Many growers have built or purchased custom rigs for 2 or more rows.  All disease protectant chemistries (fungicides, bactericides) require complete coverage for good control.  In fact all non-systemic plant protectants require 100% coverage to work well.  Our silicon products have the same requirement, and I learned the lesson well.

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