Foiling Fungicide Failure: Fungicide Applications

WHAT CAUSES UNDESIRABLE RESULTS? Quite a few problems can derail a fungicide application. Failure to carry out any of the preparatory steps properly can thwart results. Determine the culprit of fungicide failure so steps can be taken to prevent future problems. While reading through the following causes, think back to a recent fungicide fiasco. One of these – or possibly even a combination of them – could be responsible.

Incorrect Disease Identification – This is commonly overlooked because no one likes to admit to mistakes. Diseases are probably the most difficult problems to diagnose because of the size and vague nature of the indicators and the variability from one season to the next. For instance, there are at least 10 different maladies that cause identical symptoms in trees. In turf, the blighted area may look like melting out, but closer inspection may reveal drought stress, irrigation system inefficiencies or bluegrass billbugs. Buy several turf and ornamental disease identification books and place one in each company vehicle.

Formulation Choice – Most fungicides specify which part of the plant should be contacted with the spray tank mixture. Leaf diseases, such as dollar spot and bipolaris leaf spot, call for thorough foliage coverage. Root and crown rot diseases, including summer patch and necrotic ring spot, are most effectively controlled with applications that move downward through thatch and protect plants’ roots. As a result, liquid or water dispersible granule formulations are most effective for leaf diseases, while root and crown maladies should be treated with granular products.

Coverage Gaps – When applying fungicides, don’t assume every square inch of turf has the same product application rate. Diseases on irregular and/or linear turf patches could be caused by the applicator leaving gaps in the spreader coverage or spray pattern. Reduce gaps in coverage by using spray pattern indicators that help visualize the delivery of the product (For more information, see Spray Pattern Pointers on page 80).

Second Application Needs – When weather conditions are favorable, diseases such as brown patch or pythium may require additional fungicide applications at regular intervals after the initial application. Read pesticide labels and check with suppliers to determine if additional applications are necessary, but most importantly, pay close attention to weather reports. Nighttime temperatures, relative humidity and wind speeds influence disease management. For instance, higher temperatures, humidity and excessive rainfall can lead to disease.

Equipment Calibration – Don’t assume equipment applies the desired amount of herbicide every time. Orifices get plugged or worn, nozzles get bent or crushed; even lopsided tires can cause inaccuracies.

Spray checks can alert LCOs of problems. This is an honest look at the output of a sprayer or spreader, and it can be very revealing. For boom sprayers, attach glass jars underneath each nozzle, let the sprayer run for a minute, then measure the amounts in each jar. In most cases, some will put out the right amount, some less than desired, some more than desired, and some will be completely plugged. For dry spreaders, mark off a 1,000-square-foot turf section. Weigh out the correct number of product pounds and make the application. If there isn’t enough to cover the area, or if a considerable amount remains in the hopper after the area is covered, then calibration, adjustment or replacement is necessary.

Application Timing – Timing is critical. Following the integrated pest management philosophy, most fungicides are applied when conditions favor the development of a particular disease, and before the expression of full-blown symptoms. If your client calls you to look at a fungus in the lawn and you arrive on-site to see a heavy summer patch infection, control options are limited since the roots and crowns are already rotten and nonfunctional. However, if a client calls in the spring and wants to prevent the demise of his or her lawn, you can look in back records to find a history of summer patch problems and make a preventative application for it during the infection phase, rather than the "too late" symptom expression stage. (For timing on specific diseases, see Timing Tips on page 54).

Drift – Drift is the physical movement of the fungicide away from the intended target site during the application. If the drift is too great, the concentration is reduced and the fungicide will fail. However, the larger concern with drift is the negative effect the application will have on plants or people adjacent to the sprayed area. Drift can be reduced if fungicide applications are made when wind speeds are 5 mph or less.

Application Error - This is one of those unfortunate situations where the applicator simply didn’t understand which area to treat or which tree to spray at a customer’s home. Communication skills can be enhanced through simple techniques, such as restating the directive, drawing maps and writing instructions in understandable terms.

Improper cultural practices - In some situations, LCOs inherit problems that stem from previous, poor management regimes. These involve fertilizer amount, formulation and timing, lack of aeration, improper cut height, erratic irrigation and so on. For example, consider mowing height, especially with control of foliar turf diseases. The best control strategy calls for applying the fungicide between mowings instead of beforehand, so treated tissue isn’t removed before the active ingredients can get to work on the fungus, or just after a mowing when the turf has a reduced foliar surface for the fungicide to contact and work on.

Ignoring cultural practices stresses turf and ornamentals, lowering their resistance to fungal infections. Weather factors, such as rain, sun and wind, also influence product effectiveness, and must be considered.