Evaluation of Biorational Pesticides for use in Arboriculture

Pine needle scale

Scots pine (Pinus sylvestris)(1.5-3 m tall) growing in Christmas tree plantations infested with a pine needle scale (Chionaspis pihifoliae) were used for evaluating efficacy of products against scale crawlers and settled first stage nymphs. Treatments (Table 1) were applied 6 May 1986, 21 July 1987, or 18 May 1 988 to coincide with the end of crawler hatch. A KWH backpack mistblower operating at half-throttle on aperature setting 3 was used to deliver enough finished spray to thoroughly wet the foliage. Conditions on spray days were 24°C with 16-32 kph winds (‘86), 34°C with a 6-16 kph breeze (‘87), and 13 °C with 16-25 kph winds (‘88). Sky conditions varied from cloudy in 1986 to sunny in 1987 and overcast with threat of rain in 1988. In all years, treatments were applied to 4 single-tree replicates. No rainfall occurred for at least 24 hr in 1986 and ‘87; light rain (less than 0.25 cm) fell 2 hr after sprays had dried in 1988. Treatment effectiveness was evaluated ca. 2 weeks after application by removing five needle fascicles from at least three locations within each sprayed tree. Needles were placed in coin envelopes and transported in a cooler to the laboratory where percent mortality was assessed with the aid of a dissecting scope. Viability of the first 20 nymphs encountered on each of 5 fascicles was determined.

Pine tortoise scale

Scots pine (1-2 m tall) growing in Christmas tree plantations infested with pine tortoise scale (Toumeyella parvicornis) were used for evaluating efficacy of insecticides against mature scales. In 1985, sprays were applied 26 March when only mature female scales were present. A CO₂ compression sprayer at 40 psi with a single TeeJet SS8004 flat-fan nozzle was used to deliver sprays to run-off on four single-tree replicates. Temperature was 7-10°C with winds of 16-23 kph. Treatment effectiveness was evaluated 9 April by removing three infested twigs from each tree and evaluating mortality using a dissecting scope. In 1986, a similar, infested plantation of Scots pine was sprayed, this time with a KWH backpack mistblower operating at aperature setting 4 and spraying to runoff. Sprays were applied to three single-tree replicates per treatment on 25 April. Conditions while spraying were sunny, 23-25°C, with winds of 16-23 kph. Treatment effectiveness against mature female scales was evaluated 9 May in the aforementioned manner. In 1986, residual impact of treatments on crawler establishment was evaluated 23 June by removing five needle fascicles near the twigs infested with mature scales from each tree and counting the number of settled first nymphs with the aid of a dissecting scope.

Birch aphid

Japanese white birch (Betula platyphylla japonica (5.5 m tall) growing in an ex-perimental birch plantation at The Ohio State University, Ohio Agricultural Research and Development Center near Wooster, were chosen for evaluating efficacy of dormant sprays against newly hatched nymphs of birch aphid Euceraphís betulae). A CO₂ compression sprayer at 40 psi with a single TeeJet SS8004 flat-fan nozzle was used to apply ca. 300 ml of finished spray to an infested branch of four, single-tree replicates per treatment. Application was made 12 April under sunny skies at 18°C and a breeze of 8-16 kph. Treatment effectiveness was evaluated 15 April by counting the number of live nymphs on 12.5 cm sections of three terminal twigs for each replicate.

Spruce spider mite

Fraser fir (Abies fraseri) (0.5-1.5 m tall), growing in Christmas tree plantations, were used to evaluate pesticides against spruce spider mite (Oligonychus ununguis) in 1987 and ‘88. Four heavily infested single-tree replicates were sprayed to runoff with each treatment, using a KWH backpack mistblower at halfthrottle and aperature setting 3. The first application in 1987 was made 14 July under partly cloudy skies at 21 °C with a 16-25 kph breeze. Trees receiving two applications were sprayed again on 24 July under sunny skies at 26°C with a 0-10 kph breeze. Treatment effectiveness was evaluated 1 week after the second application by removing four, 10-15 cm long, lateral branch tips from each of the trees. Plant material was placed in plastic bags and transported in an ice chest to the laboratory. Samples were then processed immediately by passing twigs through a mite brush six times to dislodge mites to a rotating glass plate coated with Tween-20. Living mites were counted with the aid of a dissecting scope. In 1988, the first application was made to all treatments, except Margosan-O, on 6 June under sunny skies at 29°C with a breeze of 8-16 kph. Margosan-0 was applied 15 June when second applications were made for other treatments. Conditions were sunny at 31 °C and no breeze. Treatment effects were evaluated 2, 4, and 6 weeks after the second application by removing five twigs from each tree and processing them as above.

Eastern tent caterpillar and fall webworm

Flowering fruit and shade trees growing at the OARDC and infested with fall webworm (Hyphan-tria cunea) were used to evaluate efficacy of selected insecticides against caterpillars up to 25 mm (1 inch) long. A KWH backpack mistblower operating at half-throttle and aperature setting 3 was used to spray the web and surrounding foliage in each of three single-tree replicates per treatment. Application was made 19 August 1987 under sunny skies at 22°C and no breeze. Treatment effectiveness was evaluated 5, 8, and 14 days posttreatment by visually examining nests and assessing larval mortality. The same procedures were used to evaluate candidate insecticides against eastern tent caterpillar (Malacosoma americana) infesting chokecherry (Prunus virginiana) growing along roadsides in Wayne County, Ohio, in 1988. Application was made 11 May under sunny skies at 16°C with a 24-32 kph wind. Efficacy was determined as above.

Gypsy moth

Containerized northern red oak (Quercus rubra) seedlings (1-0) growing in a greenhouse were sprayed to run-off with a CO₂ compression sprayer with a SS-8804 flat-fan nozzle at 20 psi. In 1986, plants were sprayed before 4th instars were placed on seedlings. In 1987, five 4th instars were placed on plants prior to application. Forty-eight hours later, an additional five larvae were placed on each treated plant. Following application, larvae were constrained by securing a 1 gallon Fonda carton around the seedling in each container. The top of the carton was replaced with nylon organdy for ventilation. Larvae and foliage were observed daily until final mortality counts were made 72 (‘86) or 96 h after application or placing larvae on treated foliage.

Japanese beetle

Pyracantha (Pyracantha angustifolia) ‘Gnome’ (0.2 m tall) growing in containers were used to evaluate efficacy of insecticides against Japanese beetle (Popillia ļaponica Newman) adults. A CO₂ compression sprayer with a TeeJet SS-8004 flat-fan nozzle was used to apply foliar and topical sprays to runoff. Foliar applications were made at 40 psi on 24 July under sunny skies at 29°C and a 16-25 kph breeze. Treatments received ca. 0.8 cm of rainfall 4 hours after sprays were applied and 2.0 cm additional rainfall throughout the test period, along with 3.8 cm of weekly overhead irrigation after first samples were removed. Foliar sprays were evaluated by removing two 10-15 cm twigs from each plant at specified intervals. They and 5 field-collected beetles were placed in 1-liter Fonda cups with mesh tops. Residual efficacy of insecticides was evaluated 1, 3, 7, 14, and 21 days after foliar sprays were applied by allowing adults to feed on sprayed foliage for 48 h. After 48 h, moribund adults were placed on unsprayed foliage, and final percent mortality was assessed 48 h later. Topical applications were made at 15 psi on 27 July under sunny skies at 27°C and an 8-16 kph breeze. In topical tests, three 10-15 cm twigs were placed upright in culture tubes with the cut end in water. Five adults were placed on each twig, and sprays were applied to runoff in the aforementioned manner. Adults and twigs were immediately transferred to 1-liter Fonda cups fitted with mesh tops. Treatment effectiveness was evaluated as above. All treatments were replicated 3 times.

Data were analyzed by analysis of variance. Treatment means were separated using Duncan’s new multiple range test (Duncan 1955).

Pine needle scale

Safer insecticidal soap caused high mortality of settled nymphs in all three years of evaluation, and was consistently more effective than standard, conventional pro-ducts. Murphy’s insecticidal soap at the 1 % rate was more effective than Orthene in 1987 and provided relatively good control at the standard rate of 2% (Table 1).

Results from three years of testing indicate that insecticidal soaps are excellent products for controlling crawlers and settled first stage nymphs of pine needle scale. Our results suggest that their timing may be less important than with conventional products. However, applicators should always apply these and other pesticidal substances when target insects are in their most vulnerable stage. Sprays for armored scale insects, like pine needle scale, Euonymus scale (Unaspis euonymi), and oystershell scale (Lepidosaphes ulmi), should always be applied soon after crawler hatch has ended but before they molt to the second stage. If crawler hatch extends beyond about 5 days in the South or 7 to 8 days in the North, two applications at 5 to 10 day intervals may be required to achieve an acceptable level of control.

Horticultural oils, sometimes in combination with a conventional insecticide like Ethion, have been used for control of scale insects for decades. In our 1986 trial, 2% horticultural oil (Sunspray 6E) was as effective as insecticidal soap and better than the standards Dursban, Orthene, and Sevin (Table 1). Baxendale and Johnson (1) used Sunspray 6E at 3% against soft and armored scales, both after crawler hatch was advanced and just as or before hatching commenced. In all trials, the treatment caused excellent control of crawlers and settled first stage nymphs; unhatched eggs were killed as the oil penetrated beneath the protective covering secreted by the female scale. Since insect metabolism is extremely high during the late stages of incubation and early crawler activity, oils can be expected to be most effective at that time, if indeed their mode of action is to interfere with gas exchange. More tests are needed to evaluate effectiveness of lower concentrations of horticultural oils to determine their minimum dosage and the window of opportunity against both armored and soft scales.

Pine tortoise scale

None of the insecticides evaluated against overwintered females in early spring 1985 was effective, as measured by our evaluation procedures (Table 2). Application of soap and oil in late April, 1986, again failed to cause obvious mortality of overwintered females. However, later foliage sampling indicated that Sunspray 6E significantly reduced the number of first stage nymphs on adjoining branches after hatch was complete. This result indicates that oils may cause sublethal effects that eventually provide population reduction through means other than direct toxicity to sprayed life stages. Tests by Baxendale and Johnson (1) would seem to substantiate this speculation.

Birch aphid

Even high concentrations of insecticidal soap and horticultural oil, used alone, failed to signficantly reduce aphid numbers on branches of white birch soon after overwintered eggs had hatched in 1985 (Table 3). However, a combina- tion of Safer soap and Scalecide caused a signfi-cant reduction in aphid numbers. Since this test was performed on branches, rather than entire trees, it is possible that within-tree migration of wingless aphids during the 3 days from application to sampling resulted in a conservative estimate of treatment effects. This work needs to be repeated by spraying entire, isolated trees with each product. Furthermore, it appears that combinations of soaps and oils deserve further evaluation as aphicides. Since aphids and resultant honeydew are common problems in environmentally sensitive areas, including patios, swimming pools, and ponds, these biorational products need to be tested in novel ways to maximize their utility in landscape management.

Spruce spider mite

The mite population diminished naturally soon after the second application in 1987, even on the unsprayed check plants, precluding critical evaluation of treatment effects. However, the limited data obtained indicated that pesticidal soaps can not be expected to provide control of spruce spider mite unless at least two applications are used (Table 4). Although a single application of Plictran was effective, it has been removed from the market and is no longer available to landscape managers or producers of nursery crops or Christmas trees. Other conventional miticides like Kelthane also require two applications at a 6 to 10 day interval, depending upon local temperatures.

Even two applications of Safer insecticidal soap were ineffective by themselves in 1988, but the soap showed promise as an acaricide when combined with cotton seed oil (Table 4). Again, mite populations diminished soon after the 2-week sampling, precluding further evaluation of residual effectiveness of treatments. Sunspray 6E was ineffective against spruce spider mite, but should be evaluated at higher concentrations and in combination with soap and other products before it is discarded as a miticide. In a small-scale test with spruce spider mite on Hemlock (Tsuga canadensis ), Baxendale and Johnson (1) achieved excellent mite control with a single application of 3% Sunspray 6E. They had similar results against spider mites on deciduous landscape plants.

Defoliators

Soaps and oil sprayed on webs (tents) and surrounding foliage of infested trees in the field were ineffective against eastern tent caterpillar and fall webworm (Table 5). However, when soaps were applied topically to 4th instar gypsy moth on containerized oaks in the greenhouse, they provided acceptable larval mortality (Table 6). In the same test, when larvae were placed on foliage previously treated with soap, the treatment was ineffective. This indicates that if soaps are to be effective against lepidopterous defoliators, application should be made when larvae are small and before webs provide significant protection from contact sprays. Since there is no residual effectiveness, even when larvae eat treated foliage (see Table 6), thorough coverage of all plant surfaces is critical to efficacy.

Similar results were obtained with soaps against Japanese beetle adults. When foliage was sprayed before beetles were placed on plants, soaps were ineffective. However, in 1988 and 1989, when the beetles were contacted with Safer insecticidal soap, all of them died within 24 hours. If thorough coverage can be achieved and repeated applications are feasible, it appears that insecticidal soap is a viable treatment for controlling Japanese beetle adults in landscape management. This usage is probably more amenable to use by homeowners than arborists, since repeat applications are costly and sometimes impossible to provide to a large number of customers on a timely basis.

Sunspray 6 E was ineffective against Japanese beetles, whether applied to foliage or when sprayed directly on the adults. Margosan-0 was ineffective as a foliar spray against this important pest.

The combination of natural pyrethrum and B.t. provided excellent control of 2nd instar gypsy moth within 3 days and 4th instars within 5 days (Table 6). This combination product may have utility in urban forest pest management. Natural pyrethrum, singly and in combination with biora-tional and conventional pesticides, deserves further attention as efforts are made to reduce usage of conventional pesticides in urban and community forests.