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Ornamentals and Turf |
Some of the more spectacular galls of oaks occur in the spring and early summer. Gall wasps have alternating generations in which the offspring resemble the grandparents, not the parents. Not only that, but the galls of the two generations are usually quite different. One generation produces stem galls in which development takes two or three years and the other generation produces leaf galls in which development takes less than a growing season. Adults sometimes emerge from the stem galls in mid-winter and lay their eggs in the buds. Adults from leaf galls emerge in late spring and lay their eggs in stems (or roots or immature acorns).
Roly-poly galls are caused by larvae of a gall wasp in the genus Dryocosmus. Roly-poly galls are also called succulent oak galls. The leaf galls of the roly-poly gall wasp are amazing in that the wasp grub develops inside a seed-like structure that rolls around freely inside the hollow sphere of the gall, hence the name roly-poly galls. The biology of roly-poly galls has not been described in detail.
Small, leafy or flower-like galls on live oak are caused by the gall wasp, Andricus quercusfoliatus. Females lay their eggs in the buds, which causes the buds of live oaks to form the galls inside of which their larvae mature. Dryocosmus floridensis causes a leafy gall on red oak.
Various sorts of knot galls, horned galls, potato galls, and gouty galls on the leaves and twigs of oaks are caused by gall wasps in the genus Callirhytis. These tiny wasps apparently lay their eggs on the limbs of oaks and their larvae cause galls that eventually may cause the stem to die from the gall outward. The gall wasp, Callirhytis quercusoperator, causes woolly galls on the catkins of oaks in which their larvae develop inside seed-like structures. When the new wasps emerge, they lay their eggs in immature acorns. Callirhytis claviger causes an unattractive stem gall on willow oak. Callirhytis crypta forms stem galls on blackjack oak. The stems are slightly swollen and if the gall wasps have emerged, their emergence holes are also noticeable.
Galls wasps in the genus Neuroterus have some of the most unusual galls. Neuroterus irregularis causes an irregular gall on the leaves of post oak. Neuroterus saltarius forms tiny galls on the leaves of post oak that are dehiscent, that is, they drop off of the leaf. A sunken scar marks the spot of the gall. If enough galls form on a leaf, the leaf may die back.
Philonix nigra causes small, spherical, fuzzy galls on the leaves of northern red oak. Large oak-apple gall wasps form galls on the leaves or leaf petioles of various red, black and scarlet oaks. These galls are up to two inches in diameter, are green tinged with red when fresh, and gradually turn brown. The wool sower gall was discussed in the April 30, 2004 issue of the North Carolina Pest News.
Control
Gall control is easy. The solution is to go fishing. Rarely do galls cause more than cosmetic damage. Granted, some trees can become unsightly. In those cases, any means within reason that can enhance the vitality of the trees could be attempted. It is known that trees under stress have more simple sugars (rather than starches) and more free amino acids (rather than more complex proteins) in the sap. Thus, stressed trees are more nutritious to the gall wasps than healthy trees. Providing an infested tree with the optimum growing condition should make it better able to compensate for the damage caused by the galls and less susceptible to the gall wasps (and other pests, too). Gall wasps also have parasites and often gall wasp populations decline naturally. Ornamentals and Turf Insect Information Note No. 5 explains the biology of gall-forming insects. Heavy pesticide application tactics have been of little value.
Now is a good time to develop a fire ant management plan and begin to implement the plan. Should you scout, bait, drench, and/or broadcast? See the North Carolina Cooperative Extension Service Publication AG-486 for more information. Texas A&M University has a great web site with information, newsletters, slides, photographs, and educational materials on fire ants.
In the spring of 2004, Phytophthora ramorum (Figure 1; Figure 2) cause of Sudden Oak Death (SOD) and Phytophthora blight in California and Europe was found on camellias at two nurseries in southern California in a region outside the regulated counties in CA. Prior to inspection of these nurseries, camellias and viburnums were shipped to more than 1200 locations in 39 states some of which were unknowingly infected with P. ramorum. Through subsequent trace-forward inspections of these locations by the U. S. Department of Agriculture, Animal and Plant Heath Inspection Service, Plant Protection and Quarantine (USDA APHIS PPQ) working in cooperation with the North Carolina Department of Agriculture and Consumer Services, it was determined that eight of 44 locations in North Carolina with camellias still on site had received infected plants. A total of 54 locations in 11 states outside of California have received infected plant material as of May 2004. Federal eradication guidelines (http://www.aphis.usda.gov/ppq/ispm/sod/pdf_files/confirmed_nursery_protocol.pdf) are being followed to destroy infected plants in North Carolina and elsewhere.
What should North Carolina nurseries do to avoid future problems with this federally regulated pathogen?
Be aware of the current host and associated host list for P. ramorum.
Know the geographical source of plant material you buy.
Take steps at the nursery to minimize the impact should P. ramorum be introduced.
-- The Federal "Confirmed Nursery Protocol" (http://www.aphis.usda.gov/ppq/ispm/sod/) is very specific in the way "blocks" of infected plants are selected for destruction. A "2 meter, 10 meter rule" is applied. Plants that are hosts or associated hosts where P. ramorum has been detected will be destroyed until a distance of 2 meters (about 6 feet) of non-host or plant-free zone is encountered.
-- For most nurseries the "2 meter, 10 meter rule" means that only driveways not walkways will be wide enough to meet the 2 meter rule. Thus very large "blocks" of host and associated hosts could be destroyed by the regulation rules.
-- Therefore, it is important to re-think the way you lay out your nursery "blocks" so that you include "blocks" of non-hosts such as Japanese or Chinese hollies every so often. How often depends on how many host and associated hosts you are willing to see destroyed should P. ramorum be detected in that block.
-- Hosts and associated hosts within 10 meters of the non-host or plant- free zone will be held for 90 days and inspected twice for evidence of P. ramorum. During this 90-day period no fungicide may be applied to these plants.
Review your Integrated Pest Management (IPM) plan for your nursery.
More information on Sudden Oak Death and Phytophthora ramorum in nurseries can be found at the following web sites:
Spring seems to have slipped right past and we went directly to summer! The weeds are responding to the wonderfully warm weather.
Many of you know that glyphosate works best on many woody weeds when the plants are in flower. Some of these woody weeds are in flower now in central North Carolina, including multiflora rose, Japanese honeysuckle, and poison ivy. These are hard to kill weeds but now is the best time to spray with glyphosate. A table of recommended applications times for optimum weed control with glyphosate is available in Horticulture Information Leaflet 648.
Summer grasses are just getting a start, too. Summer annual grasses and perennial grasses can be controlled selectively with postemergence grass herbicides (Vantage, Fusilade, Envoy and Acclaim). The following article contains a summary of postemergence control of grass weeds in landscape and nursery plantings.
Annual and perennial grasses can be selectively controlled in most broadleaf crops and landscapes using postemergence herbicides that control only grasses B chemicals often referred to as postemergence graminicides. There are four graminicides labeled for use in horticultural crops B fenoxaprop, fluazifop-p, sethoxydim and clethodim. Each graminicide is systemic (translocated) and has short-term soil residual (about 2 weeks). Although each herbicide kills grasses in the same way (acting upon the same site of action), they differ in their effectiveness on grass weeds, safety on crops, and labeled uses.
FOPS and DIMS
The four postemergence graminicides can be grouped into two chemical classes sometimes referred to as the FOPS and DIMS. Fenoxaprop and fluazifop-p are chemically similar and are often referred to as the FOPS. Sethoxydim and clethodim, the DIMS, are chemically similar to one another, but quite different from the FOPS. It is important to know to which chemical class the herbicides belong because crop selectivity differs between the classes.
FOPS:
Fenoxaprop - Acclaim
Fluazifop-p - Fusilade DX, Fusilade II, Ornamec
DIMS:
Sethoxydim - Poast, Vantage, Take-Away
Clethodim - Select, Envoy
Acclaim is labeled for postemergence control of summer annual grasses in cool-season turfgrasses and landscape beds. It is most commonly used to control crabgrass in fescue or bluegrass turf. It is not as effective as the other three graminicides on perennial grasses. While safe on most broadleaf crops and ornamentals, it has been shown to severely injure certain cultivars of prostrate junipers and some azaleas.
Fusilade II is labeled for annual and perennial grass control in ornamentals, a few vegetable crops and some fruit crops. Ornamec is a special label for use in landscape ornamentals. Fusilade II controls perennial grasses including bermudagrass and johnsongrass, but is weak on fescues. Under certain conditions Fusilade II can be applied to tall fescue to control other weedy grasses, but high rates can kill tall fescue. Like Acclaim, Fusilade II can be safely applied over the top of most broadleaf plants but has injured certain cultivars of prostrate junipers and azaleas.
Vantage/Poast control both annual and perennial grasses. Poast is labeled for many vegetable and fruit crops whereas Vantage is labeled for use in ornamentals. Poast/Vantage has controlled crabgrass better than Fusilade II or Envoy/Select, but is generally considered to be weaker on perennial grasses. Varietal differences in crop susceptibility have not been reported with Poast/Vantage.
Envoy/Select is the only postemergence graminicide that controls annual bluegrass. It is generally considered to be one of the better graminicides on perennial grasses including bermudagrass and fescues. The newest of the graminicides on the market, Select / Envoy is not currently labeled on many crop species but the lists of labeled crops is expected to be expanded in the near future to include many vegetable crops and woody ornamentals.
Getting the Most Out of Graminicide Treatments
Use the right product at the right time. As stated above, the herbicides differ in their effectiveness on several weeds. Select/Envoy is the only one that controls annual bluegrass. See Table 1 for a comparison of post-graminicides on some common grass weeds. The graminicides are more effective when applied to young, actively growing weeds, and less effective when applied to large, mature weeds. For example, Acclaim is most effective when applied to young plants (1 to 3 tillers in size). At larger growth stages higher doses and repeated applications might be required. Similarly, Fusilade II and Select/Envoy are more effective on bermudagrass in early summer (with 6 to 8 inches of new growth) than in late summer when plants are flowering.
Table 1. Comparison of postemergence graminicides.
************************************************************* Grass Acclaim Envoy Fusilade Vantage ************************************************************* S. A. grasses G G-E G-E G-E Annual bluegrass P G P-F P-F Downy brome ? F-G F-G ? Bermudagrass P G G F-G Fescue P F P P Johnsongrass G-E G-E G-E G Quackgrass P G G F-G ************************************************************* Control rankings: E = excellent, G = good, F = fair, P = poor
Table 2. Recommended optimum times for treatment with postemergence graminicides for several common weeds.
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Weed Recommended Alternative
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Annual bluegrass Mid-Fall Mid-Spring
Downy brome Mid-Fall Mid-Spring
Crabgrass 1-Tiller Up to 5 Tillers
Johnsongrass Spring Late Summer
~ 6 inches new growth
Bermudagrass Late Spring Summer When
~ 6 inches new growth Actively Growing
Quackgrass Spring Late Summer
~ 6 inches new growth
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Table 3. Ornamental plant safety.
************************************************************* Ornamental Acclaim Fusilade Envoy Vantage ************************************************************* Junipers Dir* Dir* OT OT Bar Harbor Jun. No No OT OT Azalea OT Dir* OT OT Vinca minor OT OT OT OT Begonia OT OT* OT OT Pansy ? ? OT OT* Blue fescue OT No No OT ************************************************************* OT = over the top application; Dir = directed application; * = on certain varieties
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Last modified on May 17, 2004 by Stephen J. Toth, Jr.