During the growing season, we offer many suggestions about disease control—some to be initiated immediately and some to be done at a later date. Most of us have good intentions of following up on such matters but become too busy and put the job off. Here are a few suggestions on disease control for the landscape. Most steps should be taken this winter, so make a note on your calendar now.
Please don't follow every one of these recommendations unless you have had problems with these diseases. Why fix something that is not broken? In a few cases, spraying a fungicide now will prevent problems in the spring. In other cases, late winter applications are suggested. I would particularly recommend the following practices to those who have had repeated problems with any of these specific diseases. The use of fungicides for these particular diseases will serve as protectants to slow or discourage fungal development in the dormant season.
If you've had problems in turf areas with either gray snow mold (Typhula) or pink snow mold (Fusarium), you should apply a protectant fungicide now--before the first snow cover. These snow molds develop on turf that is under a layer of snow for an extended time, under areas compacted by snowmobiles, snow drifts, or snow piles, or in areas that frequently freeze and thaw under the cover of snow. Because the fungicides that control Typhula are often different than those that control Fusarium, refer to page 14 in the Illinois Commercial Landscape and Turfgrass Pest Management Handbook, 1998-1999. In some cases, repeat applications during midwinter thaws may offer increased protection against these fungi. Follow label directions carefully.
The Taphrina diseases also warrant use of dormant-season sprays. This was a big year for oak leaf blisters (see issue nos. 3 and 4) and peach leaf curl (see issue nos. 2 and 3). Both diseases are caused by Taphrina, and both can be controlled with one fungicidal application in late winter or early spring before buds begin to swell. Don't wait until next spring when symptoms show; sprays after budbreak are ineffective. If you've had problems with leaf curl on peach, nectarine, ornamental Prunus species, or oak in the past, mark your calendar now to spray a dormant fungicide in February or early March. Many fungicides are listed on page 99 of the current Illinois Commercial Landscape and Turfgrass Pest Management Handbook and on page 35 of the Illinois Homeowners' Guide to Pest Management.
Black knot of stone fruits (issue no.12) occurs on cherries, plums, and ornamental Prunus species. The disease can be controlled using a combination of pruning and fungicide applications. Mark you calendar to prune in February. Remove all knots from the tree and burn, bury, or remove them from the site. (Actually, you can do this any time the tree is dormant, but if you wait until February you'll be able to see all of the new knots, some of which will not be visible now.) Apply a dormant oil at bud swell. Many copper fungicides are labeled for use against black knot. Be certain to read the label carefully to ensure that the copper fungicide you select lists the host and disease targeted. Copper fungicides must be used in the spring to continue to protect against this fungus.
Bacterial leaf spot of stone fruit trees (issue no. 12) was another common disease in 1998, mainly as a result of the excessive rains. A copper fungicide applied once in late dormancy up to late bud swell will help considerably in controlling this disease. Balanced fertility will also greatly aid in disease control.