This gall is the hackberry nipplegall on hackberry and is caused by a psyllid (looks like a miniature cicada). Adult psyllids emerge in spring from leaf litter to mate and laid eggs on new leaves. Nymphs feed on leave throughout summer and cause the distinctive galls on the undersides of leaves. Adults emerge in September. Most galls only cause aesthetic injury and do not kill their host. Chemical control is not recommended. Avoid destroying leaves in fall, since many beneficial wasps parasitize the nymphs and overwinter in the galls. Parasitoids are common and kill up to 50% of nipplegalls.

Janet J. Knodel, Extension Entomologist

janet.knodel@ndsu.edu

Growing season flooding is detrimental to trees as the lack of soil oxygen causes roots to die. Many species cannot withstand more than 4 – 6 weeks of flooding. North Dakota Forests Service foresters recently toured the flood damaged areas of Minot. The purpose of the tour was to assess the impacts of this year’s historic flood on the survival of trees and forests within the area. Officials visited Oak Park, Roosevelt Park Zoo, Jack Hoeven Park and several neighborhoods within the vicinity.

Despite speculation of catastrophic tree and forest losses, foresters felt optimistic following the tour. Many of the mature, tall trees have withstood the weeks of inundation and appear to be recovering in areas where the water has receded. Trees most impacted by the flooding include recently planted and small trees that were completely inundated by water for several weeks. Many of these small trees and shrubs are dead. Foresters believe that some deciduous species of trees and shrubs may sprout back. Conifers (evergreens) exhibited significant lower crown injury where water covered the branches. These branches are unlikely to grow back.

Survival is speculative for trees growing along the channel where the water remains high as many tree species cannot withstand more than 6 weeks of flooding. Similar affects have been observed along the Missouri River from Garrison dam to Lake Oahe and along the Red River. Many ash and box elder trees along the Red River are beginning to fade as high channel flows have kept these trees inundated since spring.

The North Dakota Forest Service has begun assessing flooded trees and forests along the Souris and Missouri Rivers utilizing geospatial tools and is prepared to provide technical assistance to managers and decision makers. This preliminary assessment can be viewed at: http://www.ndsu.edu/pubweb/media/geoscience

For more information on the effects of flooding on trees, please go the North Dakota Forest Service at: http://www.ndsu.edu/ndfs/

Michael Kangas - North Dakota Forest Service

Michael.kangas@ndsu.edu

Large-scale defoliation by this pest has not been previously recorded in the Turtle Mountains.  Large aspen tortrix is second only to the forest tent caterpillar in its ability to reach high levels of infestation and defoliate aspen forests.  This native defoliator has also been observed in North Dakota counties north of Interstate 94.

Large aspen tortrix commonly defoliates tens of thousands of acres of aspen forests in Alberta, Ontario and the northern United States and is found throughout the natural range of aspen.  Similar to the more well-known forest tent caterpillar, populations of the large aspen tortrix have been observed to build up to very high levels, which persist for two or three years before the population crashes.  It is not uncommon for large aspen tortix and forest tent caterpillar to be found defoliating trees in the same area.

The large aspen tortrix overwinters as an immature larva in a web-like protective structure called a hibernaculum.  Larvae emerge from their hibernaculum as aspen buds begin to swell, they burrow into the buds and begin feeding on leaf tissue.  This leads to shot-holing and deformation of emerging leaves.  When aspen leaves expand the black-headed, dark green larvae roll and web together multiple aspen leaves, which they feed on and use for shelter until they are ready to pupate in early- to mid-June.  When mature, the larvae form a black shiny cocoon and emerge as adults in late-June or early-July, they mate and females lay flat clusters of pale-green eggs in a shingle-like pattern on the upper side of aspen leaves. Newly hatched larvae typically form unsightly webs as they move, feed and rappel down from the canopy representing a nuisance in recreation areas.  In infestation areas larvae have been known to feed on any and all leaf tissue, including understory plants.  In autumn, larvae congregate at the base of trees and form overwintering hibernacula in bark crevices.

Management of large aspen tortrix is only warranted on high-value and landscape trees.  The commercially available biological pesticide Bt (Bacillus thuringiensis) is effective in controlling this pest.  The North Dakota Forest Service will continue efforts to monitor the extent of aspen defoliation in the Turtle Mountains.   Inquiries about the large aspen tortrix can be directed to Aaron Bergdahl, ND Forest Service, Forest Health Specialist, at Aaron.D.Bergdahl@ndsu.edu or (701) 231-5138.

 

Aaron Bergdahl - Forest Health Specialist

The most-common disease pests of apples are fireblight, apple scab and black rot canker.  Black rot canker has been the most common issue, and the rest of this article will cover this disease and the associated problem known as frogeye leaf spot.  For more information about fireblight and apple scab, see the NDSU Extension publication “Insect and Disease Management Guide for Woody Plants in North Dakota” (http://www.ag.ndsu.edu/pubs/plantsci/trees/f1192w.htm). 

Black rot is a canker disease caused by the fungus (Botryosphaeria obtusa).  When the fungus infects stems or branches, it causes cankers which tend to grow more quickly along the length of the branch, compared to going around the branch.  A canker will typically be sunken, have darkened bark, and have small bumps that are the fruiting bodies of the fungus.  As the canker develops and expands around the branches, the leaves on the girdled branches will turn bright yellow and fall to the ground, even in the middle of summer (Figure 1).  As the canker continues to develop, entire branches or stems will be girdled and killed. Infections can also occur in the outer bark, which is dead. Outer bark infections are not sunken and cause no damage, but contain fungal fruiting bodies that can serve as a source of spores that cause new infections. Infections in the outer bark can develop into cankers if the tree is wounded or stressed.

The fungus also causes a leaf disease called frogeye leaf spot (Figure 2).  Frogeye leaf spots are typically chocolate brown with a dark ring around the edge of the spot, and the margin of the spot is sharply defined.  The infections on leaves typically occur early in the season and take place during cool, wet weather.  If there are several leaf spots, or if leaf spots occur near the leaf petiole, the leaf will turn yellow and drop. 

New infections on branches and stems occur through wounds – pruning cuts, hail damage, or tissue damaged during the previous winter. While old infections cannot be cured, there are several steps that we can take to prevent new infections or slow development of cankers.  Avoiding stress to the tree allows the tree to resist initial canker infection and expansion of existing cankers. Be careful to not wound the tree with mowers or weed trimmers and minimize the use of herbicides – both regular herbicides and those used in weed-and-feed formulations with fertilizer – within the dripline of the tree. If the cankers are confined to a manageable level, branches with cankers should be pruned out, several inches below the most basal portion of the canker. Do not leave branch stubs that can serve as an entry point for the fungus.  Pruning apple trees is best accomplished during the dormant season to minimize chances of infection by fireblight.  If apple trees are pruned during the growing season, applying streptomycin or a copper-based fungicide will help reduce the risk of fireblight infection.  If branches are broken during a windstorm or if bark is damaged by hail, treating the wounds with a copper-based fungicide will help reduce the risk of infection by both black rot and fireblight. Pruning of outer bark infections is not practical because they are usually too numerous and are not yet causing damage; instead, outer bark infections are best taken as an indication that care should be taken to avoid wounds and stress to the tree.  If the fruit load is very heavy, consider thinning out the number of fruits to about one apple per six inches of branch.

Joe Zeleznik - Extension Forester

joseph.zeleznik@ndsu.edu

Jim Walla - Forest Pathologist

The cause is a fungus known as ash rust (Puccinia sparganioides).  Like many rusts, the disease alternates between two host plants.  In the case of ash rust, the alternate host is cordgrass (Spartina spp.). 

Ash rust infections can cause trees to lose leaves; however, the level of infection that we find in North Dakota is typically minimal and rarely causes defoliation.  Thirty percent defoliation is considered to be the level at which stress begins in trees.  Control of the disease at this point in the growing season is not possible, as it infects only the newest tissues that are just developing.  To prevent future infections, first control cordgrass in the vicinity of ash trees.  Also, preventative applications of a fungicide with the active ingredient myclobutanil can be applied in the spring and early summer to the developing tissue.

Joe Zeleznik - Extension Forester

joseph.zeleznik@ndsu.edu

Tables 1 and 2 are adapted from the USDA Natural Resources Conservation Service (North Dakota) document “Tree and Shrub Characteristics.”

Unfortunately, not every tree or shrub species is listed.  Nevertheless, the information in the tables clearly shows that there are many more flood-sensitive species than flood-tolerant species.  As I mentioned in an earlier article, the low-oxygen environment that flooding brings will kill some trees outright, while others will suffer a great deal of stress.  This stress can weaken trees and make them more susceptible to root diseases or stem borers.

 

The leaf symptoms may not necessarily be visible on fallen leaves, since the infection that triggered leaf drop may be on a petiole or other inconspicuous location. This year, care should be taken when diagnosing ash anthracnose because ash leaves in parts of the state may have been damaged from wind abrasion rather than disease.

The pathogen that causes ash anthracnose is a fungus that overwinters in the upper parts of trees in seed samara, on twig cankers, and on any other plant part that remains attached to twigs, so raking and destroying fallen leaves and twigs may only help reduce inoculum rather than completely eliminate it. As a result, ash anthracnose is a recurring problem on ash as long as we have wet, cool weather in spring. It seems to vary in severity from one year to the next, and among individual trees. This is not surprising since the amount of inoculum can vary from year to year and from tree to tree.

If ash anthracnose is diagnosed, treatment with fungicides is usually not warranted. Fungicides are only effective as preventative treatments as leaves are expanding, so it is too late to protect trees this year. In general, ash anthracnose does not cause enough damage to stress trees in a single year, but trees that are heavily defoliated for three or more consecutive years can be stressed and susceptible to other pests that could kill them. On the upside, it may be comforting to know that trees can lose up to 25% of their foliage without major consequences in a single year. Lightly fertilizing trees that have lost a large amount of leaf tissue should help them refoliate and reduce stress. Heavy fertilization should be avoided.

Jim Walla (NDSU research plant pathologist) noted in a recent email to the Plant Diagnostic Lab that symptoms of wind abrasion on leaves “will be water-soaked green, brown, or black.” He added that of the many leaves that were recently blown off trees due to severe weather, only a few had spots typical of ash anthracnose, and most of the leaves did not appear to be infected. He advised proper diagnosis before implementing any disease management strategies.

 Kasia Kinzer - Plant Diagnostician

Kasia.kinzer@ndsu.edu

Below is an excerpt from the NDSU Extension bulletin F-1192, Insect and Disease Management Guide for Woody Plants in North Dakota (available at http://www.ag.ndsu.edu/pubs/plantsci/trees/f1192w.htm):

Brown rot (Monilinia fructicola)

Host(s): Plum, other stone fruits, and some pome fruits

Description/Biology: This fungus overwinters in mummies (dried, infected fruit) on the tree and on the ground and in twig cankers. In the spring, spores are produced and carried by wind, rainsplash and insects to blossoms, young leaves and shoots, where new infections occur. M. fructicola is not active during the summer but will infect ripening fruits in late summer and fall. Disease development is rapid in warm, wet and humid weather.

Damage/Symptoms: Infected leaves and shoots become brown as they are covered with spore masses. The most obvious symptom is the brown rot that occurs on the fruit. On green fruits, this is characterized by small, round, light brown spots. On ripening fruit, pale, ash-gray to brown, felt-like fuzzy masses of spores cover fruit. Fruit will rot in hours during wet weather. Rotted fruit may cling to the tree or fall to the ground. Brown rot may develop on fruit in storage.

Comments: Management for brown rot should begin in late summer and fall. Remove all remaining fruit, mummies, and cankered twigs. Remove or bury mummies before blossom. Captan may be used for controlling infection. The first application should be made as soon as blossoms show color. When the weather is wet and night temperatures are above 55^oF, apply the second spray at full bloom and the third spray at petal fall. Another application should be made when green fruits are fully developed but have no color. Repeat the application 10-14 days later if the weather is humid and temperatures are 60 to 80^oF.

Captan can be found in products such as Ortho Home Orchard Spray, Dragon Fruit Tree Spray, Ferti-lome Fruit Tree Spray, Bonide Captan 50W, Bonide Rose Insect & Disease Control, and Hi-Yield Captan 50% WP. If Captan is used, be sure to spray when bees are not active, as per the label instructions, because it is poisonous to them. Other fungicdes labeled for brown rot control include chlorothalonil (Ortho Garden Disease Control (Daconil 2787), Hi-Yield Daconil Lawn Vegetable Flower Fungicide, Fertilome Lawn & Garden fungicide, Fertilome Broad Spectrum Liquid Fungicide, and Bonide Fung-onil) , myclobutanil (Spectracide Immunox, Ferti-lome F-Stop Granular Fungicide, Green Light Fung-Away Systemic Granules), and sulfur (Ferti-lome Dusting Sulfur, Bonide Liquid Sulfur, Bonide Sulfur Plant Fungicide, Safer Garden Fungicide, others). (Source for homeowner fungicide information: Homeowner Fungicide Guide; author: Elizabeth Little, University of Georgia Extension Homeowner IPM Specialist; online at http://www.ent.uga.edu/pmh/Hm_Fungicide&Organic.pdf). Be sure to read, understand, and follow all label instructions when using fungicides or any other pesticides – to prevent harm to yourself, the plant, and the environment.

Kasia Kinzer - Plant Diagnostician

Kasia.kinzer@ndsu.edu

 

 

  Two needle cast diseases occur in North Dakota: Rhizosphaera needle cast and Stigmina needle cast. Similarities and differences between the two diseases exist. Symptoms of both needle cast diseases look similar to each other. The classic symptoms of needle cast include brownish purple discoloration and eventual death of  older needles, while current-year needles show no symptoms (Figure 1). Another key characteristic of needle cast is the microscopic rows of small black dots (fungal fruiting bodies) that displace the normally white stomata along the length of the underside of needles. The fruiting bodies of Rhizosphaera kalkhoffii are spherical (Figure 2) while those of Stigmina lautii have what look like microscopic hairy projections emerging from a the fruiting body (Figure 3) . The fruiting bodies of both fungi are noticeable with a 10X hand lens and are located in the needles’ stomata which are normally white. Rhizosphaera needle cast (caused by the fungus Rhizosphaera kalkhoffii) primarily infects Colorado blue spruce, while Stigmina needle cast (caused by the fungus Stigmina lautii) affects both blue spruce and Black Hills spruce.

Needle cast diseases thrive in humid, wet environments and they are more common in the north and east parts of our state. Although we have seen needle cast diseases as far west as Minot, we expect it to occur rarely, if at all, west of U.S. Highway 83. It is most common east of U.S. Highway 52 and is especially prominent in the Devils Lake basin and the Red River Valley.

 Proper diagnosis of needle cast is recommended before treatment is initiated, since other non-disease factors can cause similar symptoms. Other pests and environmental problems can cause browning and death of older needles, including normal needle death that occurs simply as a function of needle age or shading. These other causes can be easily confused with a needle cast disease. Identifying the fungal fruiting bodies in the stomata is crucial before a needle cast disease can be diagnosed and before fungicide treatments are applied. 

Needle cast diseases of spruce are treatable. Within a few years after treatment, an infested spruce tree can look beautiful again. Left untreated, a severe case of needle cast can lead to continual thinning and eventual decline of the affected tree if spring weather is conducive to infection year after year.

Needle cast diseases can be effectively controlled with fungicides containing chlorothalonil. For Rhizosphaera needle cast, two properly-timed applications per year for at least two consecutive years, and sometimes three years, is required for control. The first application should occur when the new needles are half elongated (50% elongation relative to previous years’ needle length). We usually say “around Memorial Day”, but actual timing depends on the year, the location, and the individual tree. The second application should occur three to four weeks after the first application. The timing of the two applications is the same for the second and third year. Timing of treatment for Stigmina needle cast is similar, except preliminary data suggest that the trees should be treated indefinitely, with at least two properly timed fungicide applications per year.

Proper timing of the fungicide application is critical for effective control. Spraying too early or too late will miss the stages when the tree can be protected from infection by the fungus. A lot of time and money has been wasted by applying fungicides at the wrong time. For further information on Rhizosphaera needle cast, see the NDSU Extension service publication PP-1276, “Spruce Diseases in North Dakota.” If a fungicide is used, be sure to read, understand, and follow the labeled instructions to avoid injury to the tree, the environment, or yourself.

If unsure whether a spruce has a needle cast disease, consider consulting with your local county agent.

Kasia Kinzer - Plant Diagnostician

Kasia.kinzer@ndsu.edu

Joseph.zeleznik@ndsu.edu

Aaron Bergdahl - Forest Health Specialist

Aaron.bergdahl@ndsu.edu

Three species of tent caterpillar occur in our area: eastern tent caterpillar (Malacosoma americanum), forest tent caterpillar (M. disstria), and prairie tent caterpillar (M. californicum ssp. lutescens). Host plant damage by these moth species is caused by the larvae, or “caterpillars.” Several hardwood hosts may be used, depending on the species.

Eastern tent caterpillar prefers chokecherry, though it will feed on other hardwood species occasionally. Larvae of eastern tent caterpillar are gregarious and construct tent-like nests of silk in the forks of branches and smaller trees (Figure 1). Tents are used for shelter or as resting places. Larvae forage during the day in new foliage on nearby branches. Larvae feed for 6 to 8 weeks and are about 2 inches long when mature. Larvae (Figure 2) are black and rather hairy, with a whitish-yellow stripe down the middle of the back, narrow broken orange stripes just to either side of the whitish mid-stripe, and lateral white and blue markings. Larvae disperse when mature and spin cocoons in sheltered places. Adult moths appear in late June and early July. Females lay eggs in a band-like cluster of 150 to 350 eggs around a small twig and cover the eggs with a frothy excretion called spumaline. Eggs overwinter and larvae emerge in the spring; thus, there is one generation per year. Larval feeding disfigures ornamental plants but usually does not result in permanent damage unless the feeding is severe. Tents and masses of larvae are unsightly. Eastern tent caterpillar populations usually peak every 10 years.

    

Forest tent caterpillar utilizes a wide variety of hosts, including ash, aspen, basswood, birch, cottonwood, elm, maple, and oak. Larvae emerge in the spring from overwintered eggs. Emergence coincides with the flush of host plant foliage. Larvae feed for 5 to 6 weeks and are about 2 inches long when mature. Larvae are identified by keyhole-shaped spots along the midline of the back and by broad bluish lateral bands (Figure 3). Unlike other tent caterpillars, forest tent caterpillar does not form a tent. Instead, larvae gather and spin silken mats on branches. Larvae tend to feed in wandering masses. Mature larvae form silken cocoons, and adult moths emerge about 10 days later. Females deposit 150 to 200 eggs around small twigs and cover the eggs with spumaline. Light defoliation has little effect on tree growth, but severe feeding can affect growth and cause twig mortality. In North Dakota, outbreaks of forest tent caterpillar typically last for 2 to 4 years.

Prairie tent caterpillar can utilize a variety of hardwood host, though chokecherry is its preferred host. Prairie tent caterpillar is the most common tent caterpillar species in North Dakota. Praire tent caterpillar overwinters in the egg stage and larvae emerge in the spring with the flush of their host plant foliage. Larvae feed for 6 to 8 weeks and are about 2 inches long when mature. Larvae are black with a white mid-line stripe broken into dashes, and light blue lateral stripes also broken into dahses. Like eastern tent caterpillar, larvae of prairie tent caterpillar form silken tents in the forks of branches and small trees and feed on nearby foliage. Mature larvae spin cocoons in curled leaves or in leaf litter. Adult moths emerge in mid-summer. Females lay eggs near the base of the host plant in the ground. Larval damage is similar to that of eastern tent caterpillar.

Control of all tent caterpillar species should target larvae. Actively feeding larvae are easily controlled with conventional foliar insecticides including acephate, carbaryl, imidacloprid, or any of several pyrethroids. Biorational treatments include Bacillus thuringiensis (Bt) for young larvae, insecticidal soap, and pyrethrin. Boiling water can also be poured directly on tents that contain larvae. Tents may also be physically removed and destroyed.

Patrick Beauzay, Research Specialist

Extension Entomology

patrick.beauzay@ndsu.edu

 

The mature larvae of forest tent caterpillar are easy to distinguish by the white, keyhole-shaped markings along their top sides (Figure 2).  The young larvae in Figure 1 don’t show those markings yet, though they are beginning to develop just three days later.

      

Controlling the insect was incredibly easy in this case – I clipped the ends off of three branches, removing the larvae and the egg masses (Figure 3).  However, if the infestation had been heavy, chemical control may have become necessary.  In such situations, younger larvae may be controlled by Bt.  For older caterpillars, permethrin or pyrethrins or other insecticides may be needed.  As always, when using pesticides, follow label instructions carefully.  See next article for more information on tent caterpillars. 

 

Joe Zeleznik - Extension Forester

joseph.zeleznik@ndsu.edu

However, as we gradually get into the growing season, more and more species are beginning to leaf out, and that could cause problems for some of them.  Trees that naturally grow along the rivers – cottonwoods, willows, boxelders, green ash, and others – are adapted to flooding and can be totally inundated for two to three weeks without suffering any ill effects.  Other species, such as common lilac or Colorado blue spruce, are very sensitive to the low-oxygen soil environment created by flooding. 

The most direct effect of having roots in a low-oxygen environment is the opposite of what we would expect – they don’t take in water very well and the trees actually suffer from “physiological drought.”  In the short term, leaves may begin to wilt in as little as two weeks.  Additionally, if the flood brings in a large load of sediment, root systems can be buried and a reduced-oxygen effect environment may last for years. This stress can weaken trees and make them more susceptible to root diseases or stem borers.

Some recent research suggests that applying a nitrogen-based fertilizer will help trees recover from the stress caused by flooding. The research methods that the authors used doesn’t let us give specific recommendations, but a general recommendation is to fertilize the soil around trees at a rate of 1-3 pounds of nitrogen per 1000 square feet of ground surface, per year. The fertilizer can be applied through one or several applications, but it is important to avoid overfertilizing or applying fertilizer during mid-to-late summer (July through mid-September) as this may decrease the tree’s ability to harden up for winter.

In summary, trees that normally grow along rivers are generally adapted to occasional flood events. Floods that occur during the growing season are to a certain degree more stressful than those that occur during the dormant season. By minimizing post-flood stresses to the trees, we can help them recover and thrive as well as they did before inundation.

 Joe Zeleznik - Extension Forester

joseph.zeleznik@ndsu.edu