Pest Alert

October 18, 1999

Welcome to Pest Alert. This is the final issue of the 1999 growing season. We hope that Pest Alert has been a valuable asset to you in your business, Extension Office or for you as a Master Gardener or home gardener. We would appreciate any comments you may have about the newsletter as we consider putting together issues for next year. Written comments may be directed to Pest Alert, Department of Horticulture, Forestry, Landscape and Parks, Box 2140A, Brookings, SD 57007, or you may send your comments via email to David_Graper@sdstate.edu.

Categories for topics are as follows, H - Herbaceous plants and flowers, W - Woody Plants, V - Vegetables, F - Fruit and L - Lawns.

DISEASES

W ANTHACNOSE AND OTHER FOLIAR DISEASES were a significant problem in many parts of our state this year. Whether this will carry over to next year is anyone's guess. If we experience a cool, moist spring it is likely that we will see a repeat of this year's problems. While many of these diseases do not result in tree mortality, they can certainly affect the ornamental value of the plant. Unfortunately, once the problem is noticed it’s too late for control. If the spring forecast is cool and moist and the appearance of the plant is of major concern, the application of an appropriate fungicide may be warranted.

V,H ROTATION OF CROPS. Take some time to make some notes about your gardening experiences this past season. If you made a map of your garden prior or after planting, use it to help you recall the successes or struggles you had with your garden. Perhaps some varieties were very productive while others suffered major disease problems. As the winter wears on we can start planning our flower and vegetable gardens with some disease management tactics in mind. The choices we make should reflect the diseases experienced this past year. Rotation to different plant species on a site is a good practice to manage disease organisms that persist in the soil. Avoid planting tomatoes, potatoes or other crops in the nightshade family on the same sites. They share many diseases and this year’s problem on potato could be next year’s tomato disease. Similarly, cucurbits should be planted in another location. Melons, cucumbers, and squash also share many diseases. If problems have developed with white mold on beans, peas, potatoes, sunflowers, marigolds, petunias or any of many other flowers in the garden, careful consideration must be given to rotating away from susceptible crops.

OTHER NOTES

F,W ARE YOUR FRUIT TREES PROTECTED? One of the most common calls we receive each spring comes from individuals that have young fruit trees that were girdled by rabbits or other animals over the winter. Now is the time to give those smooth barked trees some protection. One of the best is to use ½" mesh hardware cloth to make a ring around the trunk which extends from the ground up to the lower branches. Firmly attach the wire to a few small stakes at ground level to prevent the wire from moving around allowing small rodents to get underneath. Make the ring large enough so that there are several inches of space between the wire and the trunk. Another option is to wrap the trunk. There are several materials available for this task. Make sure not to wrap it too tightly and remove the wrap next spring when new growth starts on the trees. Other protective measures like repellants may also be effective. (See the last issue of Pest Alert for more information.)

W AS WE END ANOTHER GROWING SEASON it's a good time to review the pest problems that were encountered during 1999 and look ahead to 2000. Despite the bimonthly update of pests and their management, the number one problem was rarely mentioned as controls are still limited. The number one problem encountered by trees and shrubs growing throughout South Dakota is people. And here in order of frequency, as reported by service foresters of the South Dakota Division of Resource Conservation and Forestry, here are the top five people-related problems.

Planting too deep still kills far too many trees. It is not a dramatic or quick killer however, so it is often missed as the reason for a tree's decline or death. Ornamental trees should be planted so the bud union is about two-inches above the soil. Conservation s trees should be planted so the root flare is at the soil level. If trees are planted too deep, the lower trunk which is now below rather than above ground, is kept too moist and gas exchange is limited. The roots are also placed lower than they normally occur. These two conditions can result in the slow decline, perhaps several years, and generally the death of a tree.

Improper matching of plant species to site conditions. South Dakota is a land of extremes in regards to climate and soil conditions. Too often people plant trees without fully considering the tree's requirements and the site conditions. Much of the state is covered with alkaline soils and there are several trees, eastern pin oak, red maple, and river birch, that become chlorotic if grown in soils with a pH that exceeds 7.0. Numerous tree species such as sycamore, austree and even Norway maple are at their limits of winter hardiness, and with the exception of the southeastern portion of the state and a few other favorable sites, often experience winter dieback.

Improper pruning or cabling. Excessive pruning, including topping, has become a real problem, particularly in Sioux Falls. Unfortunately, most of this pruning is done by tree companies who should know better. Trees are being excessively thinned out under the guise of reducing the "sail effect". The common wisdom is by opening up the canopy the tree will experience less wind damage as some of the "sail" is being removed. While there is a small grain of truth to this, excessive thinning increases the wind, snow and ice loading on the remaining branches and can increase breakage. Topping, the reducing of the canopy to a particular height, is also sometimes employed as a measure to reduce wind damage. The weakly attached watersprouts that form around the topping cuts often snap off by wind and ice storms. The decay columns that result from these heading cuts also leave the branches more susceptible to breakage. While there are a lot of excuses given for why a tree is topped, there still is no valid reason for this practice to continue. Improper cabling can also result in tree failure. Cabling, the attachment of steel cables and rigid rods to improve the structural stability of trees, can be an excellent means of prolonging the life of a tree. However, if improperly installed, such systems can increase the likelihood of failure. The most common installation error is placing the cables at less than 2/3's the distance between the weak crotch or fork and the top of the tree. Doing so often results in breakage just below the incorrectly attached cable.

Herbicides. These chemicals, usually applied for crop or lawn protection from weeds, are blamed for far more damage than they actually cause, though there are numerous trees disfigured or killed by the misapplication of a wide range of chemical herbicides. If the advice "read and follow the label directions" was followed more often, and the label directions "do not apply in the root zone of trees" was considered, there would be far fewer instances of this people-related problem.

Lawn irrigation systems are increasingly responsible for the decline of landscape trees and shrubs. The homeowner's desire to maintain an attractive green lawn throughout the summer can keep the soil too moist for woody plants. Many of our trees and shrubs have adapted to experience slight moisture deficiencies during the summer months. Keeping the soil and lower trunk wet during this time period can increase certain fungi diseases as well as limit root growth.

While the above is not a scientific survey of problems, the trend is similar to what is being experienced in other parts of the country. The important point to consider is that the vast majority of our ornamental plant problems are not due to "bugs and crud" but "us"!

F,W ARE YOUR FRUIT TREES PROTECTED? One of the most common calls we receive each spring comes from individuals that have young fruit trees that were girdled by rabbits or other animals over the winter. Now is the time to give those smooth barked trees some protection. One of the best is to use ½" mesh hardware cloth to make a ring around the trunk which extends from the ground up to the lower branches. Firmly attach the wire to a few small stakes at ground level to prevent the wire from moving around and allow small rodents to get underneath. Make the ring large enough so that there are several inches of space between the wire and the trunk. Another option is to wrap the trunk. There are several materials available for this task. Make sure not to wrap it too tightly and remove the wrap next spring when new growth starts on the trees. Other protective measures like repellants may also be effective. (See the last issue of Pest Alert for more information.)

H BULB PLANTING is in high gear and can continue for the next few weeks. One of the most common mistakes people make is to not plant deeply enough. Most tulips, hyacinths, narcissus and other larger bulbs should be planted sot that there is about 6" of soil covering the tops of the bulbs. Smaller bulbs like botanical tulips, snow drops, crocus and others should have 3-4" of soil covering the bulbs. Generally, plant bulbs so that the top of the bulb will be covered with 2-3 x the height of the bulb with soil. Proper planting depth will ensure better winter survival, provide more timely emergence in the spring and reduce the chances of damage by rodents. Adding 3-4" of mulch to the planting bed, after the ground has frozen, will also help to delay premature flower emergence in February or March, which can result in damaged flower stalks. One final reminder, spring flowering bulbs MUST be planted this fall, you cannot hold them until spring and plant them then and expect good results. If necessary, plant the bulbs in a temporary location this fall, then replant next season after the foliage has died down.

W,F,H WATERING. If your area has not received much rain in the past month, you may want to water your trees and shrubs. The roots of many woody plants are still growing and will continue to do so until soil temperatures reach 45 F.