The old saying that “everyone talks about the weather” is certainly true when it involves landscape plant managers. Professional landscapers/arborists and their clients are always discussing how various weather factors are affecting plants. The New Jersey weather trends can often be variable from one growing season to the next. How do rain, wind and temperature changes impact plants and their corresponding insect/mite pests?

The chart below lists four weather conditions & categorizes how these conditions positively or negatively influence some of the key landscape insect/mite pests.

TABLE: PESTS AFFECTED BY SPECIFIC CONDITIONS (Source: David Shetlar, Ohio State Cooperative Extension)

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Clearwing moth borers comprise one of the most damaging groups of insect pests that attack shade trees and shrubs. Controls must be accurately timed, since larvae tunnel under the bark most of the year, where they are unreachable by most insecticides. Artificial pheromones of many of the clearwing moths found in the landscape are available. These pheromones are a synthetic of the sex attractant emitted by many insects & are commercially available and recommended for the IPM manager.

Plant manager viewing contents of clearwing moths captured in pheromone-baited wing-trap. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

This green ash tree is showing severe symptoms from banded ash clearwing moths. Too late for pheromone traps to be of value. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

Adult male clearwing moths are attracted to the pheromone-baited sticky trap that helps determine: 1) if the borers are present in an area; and 2) when to apply insecticide sprays. Pheromone traps enable landscape managers to accurately determine when the first emergence of the egg laying borers are expected so that insecticides can be timed & applied effectively to susceptible tree/shrub hosts. Spraying the bark of the tree to be protected with a long residual insecticide (i.e., such as pyrethroids) should effectively kill the young borer larvae as they hatch from eggs & attempt to tunnel into the stems or branches.

Hypothesized flight path of an adult male clearwing moth towards the pheromone trap. (Diagram: Steven K. Rettke, Rutgers Coop. Ext.)

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Removing the Tree-of-Heaven (TOH):

During the winter, arborist companies will often take advantage of the slow season and perform needed tree removal services for clients. However, these professionals know when dealing with the tree-of-heaven (Ailanthus altissima) the off-season is only a suitable time for removal if a previous herbicide treatment was applied during the late summer or early fall seasons (i.e., mid-July to mid-October). Then during the off-season, the trees can be cut & removed from mid-November thru April (Figure 1).

(Fig. 1) The cutting & removal of this cluster of tree-of-heaven trees should only be done in the winter if herbicide treatments were applied during the late summer or fall seasons. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

If a tree-of-heaven (TOH) is cut & removed without first using an herbicide & waiting at least 30 days, then the tree will respond with potentially dozens of trunk sprouts & root suckers that could emerge 50-feet from a large parent tree. Applying the herbicide during mid-July to mid-October when the tree is most actively translocating photosynthates to the root system will allow the herbicide to move further distances most effectively through the phloem. This will help reduce problems with trunk sprouts & root suckers which this tree species is notoriously known to produce (Figure 2).

(Fig. 2) Herbicides to TOH should be applied from mid-July to mid-October. The photo shows the onset of fall coloration & indicates the end of effective herbicide treatment for the season. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

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Full side view of the dog-day cicada showing the black eyes & dark green body coloration plus the clear wings with green veins. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

They Get No Respect:

For at least the past 7-8 weeks, the annual “dog-day” cicadas (Neotibicen canicularis) have been heard singing throughout many NJ locations.They tend to get little respect or media attention & could be called the “weak sister” of the far more publicised periodical cicada species that were present this past spring. The annual cicadas species have less dense populations & their lifecycles are usually 2-3 years compared to the 13-17 years for the periodical cicada species. However, the dog-day cicada emergence is not synchronized, therefore some will emerge every year. Like periodical cicadas, the dog-day males also sing to females to attract a mate. However, the dog-day cicada “electric buzz-saw” screams are not synchronized & even though each individual male is loud, they are not nearly as deafening nor continuous as the noise produced by periodical cicadas. Each male sings for only about 15 seconds & when their numbers in an area are relatively sparse, there is typically many intermittent periods of silence. When populations are more dense, then there may be a continuous non-synchronized buzzing sound that emanates throughout an area.

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This Rutgers Plant & Pest Advisory blog will review a few of the landscape summer pests specific to mostly oak trees (Quercus). The scarlet oak sawfly will be discussed first, followed by the oak spider mite & finally the oak lace bug. All three pest species have multiple generations during the summer months & therefore can be observed throughout most of the season. None of the pest species are usually considered to be life-threatening to oak hosts but they can cause significant & undesirable aesthetic injuries. However, it could be stated that these pests may have bark, but they have little bite. Therefore, with large oak trees the spraying of many gallons of pesticides would not be justified.

Spraying many gallons of a pesticide against most pests on a large oak as shown above is rarely justified. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

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Mimosa webworm early webbing of honeylocust leaflets at outer branches. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)

Mimosa Webworm (Homadaula anisocentra) = (880-1200 GDD = 1^st generation egg hatch): The overwintering pupal cocoons of this non-native caterpillar emerged as adults last June & eggs have been laid on leaflets or small twigs of honeylocust (Gleditisia tricanthos ) trees in NJ. This caterpillar also feeds on mimosa trees, but since honeylocust plantings in the urban environment are more common, we usually encountered them on these trees. Within many areas of the state, the early, initial 1st generation webbings by 1st instar caterpillars are now becoming noticeable at the outer edges of the leaf canopy.

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