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Common Queries in April

April 28, 1999
Maybe you have some of these questions. Some have clear answers and others do not.
With a disease such as apple scab, I would like to use a systemic fungicide. Which of the recommended chemicals are systemic?
If you refer to the Illinois Commercial Landscape and Turfgrass Pest Management Handbook, you will find the chemical options to protect against apple scab on crabapple listed on page 90. They include Banner, bordeaux, captan, Cleary 3336, copper, Domain, Eagle, Fore, Fungo, ISK Daconil, lime-sulfur, mancozeb, maneb, Phyton 27, Rubigan, sulfur, and Systhane. These products have been recommended after many hours of work looking through chemical company books. Most of this work was done by Bruce Paulsrud, pesticide applicator training specialist. The list includes products registered for this use and does not indicate efficacy. If you look on page 110 of the same manual, you will find a very helpful chart listing common and trade names of fungicides, as well as mobility in the plant–protective-contact, local penetrant, and systemic. The scab fungicides with systemic mobility include Banner, Cleary 3336, Domain, Eagle, Fungo, Rubigan, and Systhane.
Many fungicide labels tell us to start applications at bud break. What does this mean? Is it flower buds or leaf buds?
Bud break is the point at which buds swell and bud scales split apart. Usually, you can see some green tissue in the bud because leaves are beginning to emerge. The term refers to leaf buds. Flower buds have their own terms, including tight cluster, pink, bloom, and petal fall.
I want to get a fungicide on my tree but rain is expected. If I wait until after the rain, I will be late with the fungicide. Should I spray now?
This is a difficult decision to make. Chemicals have different rain-fast periods. And it is true that stickers applied with the chemical will help hold them to the foliage. It is never appropriate to spray during rain or mist because the chemical will wash off the foliage. Without knowing the specific rain-fast period for your chemical (call the manufacturer), a general rule is that there should be 4 hours between the application and the next rain. Bruce Paulsrud checked with a few manufacturers and found that the rain-fast period for Banner Maxx is 4 hours; for Eagle, it is 4 hours; and Rubigan is rain-fast as soon as it dries.
What is the reach-back effect?
Some systemic fungicides have a so-called reach-back effect, meaning that they can eradicate a pathogen that has recently entered a plant. For example, Eagle is a fungicide that has a reach back of 96 hours (4 days). Applying it now is the same as if you had put the active ingredient in the plant 4 days earlier. Most products do not offer this sort of reach-back benefit. (Nancy Pataky)

Author: Nancy Pataky


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