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Ornamentals and Turf |
Several growers have observed root aphids in their Christmas tree transplants this spring. There continues to be a debate as to whether or not root aphids cause a problem on Fraser fir Christmas trees. In talking with the people in Oregon, most of the growers think they are a terrible problem but the University scientists do not seem to agree. They think root aphid feeding may decrease the number of small feeder roots, but they have not, to my knowledge, observed any other problems. And these effects are only observed when there are a lot of aphids -- 200 or more per tree.
My opinion about root aphids is that they are not causing a problem unless you are finding high numbers -- 100 or more. But we see more problems on dry or infertile sites. Usually there is some other explanation for poor tree growth such as previous grub damage or just not a good site. In any case, I have not seen root aphids killing trees. It is usually Phytophthora root rot, grubs, drought or tree damage while setting.
I have been looking at insecticides for root aphid control. Some growers are using Di-Syston 15G at higher than our Section 24(c) label rate -- 50 to 100 pounds per acre. They think they are successful, but I have not made any observations to confirm that. I have considered Aphistar which has a Section 18 label in the western U. S. for root aphid control in Christmas trees. It is not labeled in North Carolina and growers can not obtain it. It does seem to control the aphids if the tree is not too damaged. I tried Vydate with about as much success a couple of years ago. But I have a research study this spring that involves all these insecticides, which will hopefully provide more conclusive information.
The Asian Ambrosia beetle flight begins in early March in North Carolina and peaks about this time of year. There are dozens of hosts for this insect. Nurseries with susceptible stock should be monitoring for entry holes and toothpick-like frass protruding from trunks. Female beetles bore into stems and young trees. Visible symptoms include wilted foliage and strings of borings that may protrude from the bark as tiny toothpicks. These strands may reach 1.5 inches if wind and rain do not break them. The beetles are present most of the year, but data from North Carolina State University indicate Asian ambrosia beetles begin activity in March and that peak flight activity stops by the end of April. Most tree death occurs at the leafing out stage. In small trunks and branches, the galleries go straight in or spiral upward from the point of attack around the stem or limb, branching upward or downward from the spiral gallery. The Asian ambrosia beetle seems to attack trees and shrubs more aggressively than native ambrosia beetles that attack mostly dead, dying or heavily-stressed plants. Because most of the boring is done in the sapwood or heartwood rather than the cambium, sometimes it is possible to save plants infested with Asian ambrosia beetles. If the damage is heavy to the main stem, it may be better to start anew if the plant is small. Dead wood or plants can be pruned and destroyed. There is evidence that beetles prefer trees that are already infested. It may be advantageous to leave these trees in place until the fall to serve as beetle "traps". It should be noted that protective treatments with chemicals are only moderately effective. Our best recommendation to nursery and landscapers is to apply Astro in early March or as indicated by trapping to try to prevent damage by the first flight of beetles. Homeowners could use a landscape pyrethroid insecticide. Ornamentals and Turf Insect Information Note No. 111 provides additional information on the biology, trapping and control of the Asian ambrosia beetle.
Boxwood leafminers adults are emerging now. This adult midge lays its eggs in the tender, pale new foliage just before leaves begin to harden. The maggots can do significant damage to the appearance of boxwood, but they usually do not cause dieback. Because the boxwood leafminer has only one generation of midges per year, treating in April and May with a foliar insecticide can be beneficial. The maggots develop in blister-like galls on the current year's leaves. Heavily-infested shrubs may become discolored and tend to defoliate prematurely. In demonstrations, Orthene and Merit have both given good control of this leafminer when injected into the soil or applied as a drench. Orthene 9.4% Emulsifiable Concentrate is labeled for leafminers on shrubs. Merit WP is labeled for leafminers on ornamentals and is marketed for homeowner use. Merit can be applied as a soil drench any time during the growing season and gives good control. Ornamentals & Turf Insect Information Note No. 16 provides information on the biology and control of the boxwood leafminer.
Already this spring we have received notices of different species of ground nesting bees in turf or landscape. These bees nest singly in tubes excavated in the ground. Commonly they nest in close aggregations, but the tunnel nests are not connected. Each female constructs her own nest without help of other bees. There is only one generation per year, so after a few weeks the activity stops until next year.
These bees do not have a nest guarding instinct as do social wasps and social bees. Just walking by the nests will not prompt the bees to attack as they do not have alarm pheromones and the instinctive behavior to attack. It may be possible to step on one while barefooted and be stung on the foot, but that is about the only hazard from these otherwise beneficial insects. These solitary bees are valuable pollinators of spring crops. We suggest that it is better to coexist with the bees because of their value in the pollination of various plants than try to eradicate them with pesticides. Ornamental and Turf Insect Information Note No. 100 contains more information on these and other ground nesting bees.
May beetles are getting an early jump on the season. These scarab beetles are among the group called white grubs or Polyphaga. Grubs spend two or three years in the soil and emerge as black or brownish beetles in the spring. They are attracted to lights and will end up on porches or banging against your windows at night. This is such a broad group that there are no specific control measures to offer. Sometimes the grubs are found in high densities in turf that the turf needs to be treated with insecticide, but there is no cure for the beetles banging against the window except to have dinner by candlelight.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on April 22, 2002 by Stephen J. Toth, Jr.
