Indiana Department of Natural Resources sent this bulletin at 06/15/2022 07:15 AM EDT
Weekly Review for June 15, 2022
This informal report by the Division of Entomology & Plant Pathology is a commentary on insects, diseases, and curiosities division staff encounter on a week-to-week basis. Comments and questions about this report are welcome and can be sent to your respective Inspector.
Ken Cote (Nursery Inspector & Compliance Officer) - KCote@dnr.IN.gov
I still have not observed bagworm in my region; however, other inspectors have reported seeing bagworm activity. During the last week I found a lot of other neat pest issues. Pine bark adelgid was found on white pine at several locations in my region. This is a white insect that occurs primarily on the bark of white pines. Typically, it is found on larger, older white pines. However, over the past two years I have been finding it more frequently in nursery stock. Damage usually only occurs at very large population numbers, but it can look objectionable to customers. Pine needle scale was also found on white pines. This pest occurs only on the needles of pines and can infest both hard pines (3 needled pines) and soft pines (5 needled pines). Look for elongated, white scales with a small tan spot on one end. This pest has two generations per year. Large amounts of this pest can cause needle yellowing and branch dieback.
Another interesting scale I encountered was the white prunicola scale. This scale often infests flowering cherries and other plants in the Prunus genus. Look for large amounts of fluffy, white wax occurring on the bark of infested trees. There will be both elongated males and rounded females that look like a fried egg occurring at the same time in colonies. There can be multiple generations a year with this pest, and heavy infestations can lead to leaf yellowing and branch dieback. Mechanical removal can help somewhat, but a residual insecticide should be used to treat large populations of this pest, especially since it can have multiple generations per year. There is a closely related species called the white peach scale that often occurs on weeping mulberry.
During the last few weeks we had some cooler temperature and lower relative humidity levels compared to what we are experiencing this week. This has led to the development of some spider mite outbreaks. I am continuing to find two spotted spider mites on roses and butterfly bush. Look on the undersides of leaves for a cream-colored mite with two black spots. This mite will feed on many different plants that are deciduous and/or herbaceous. It has not been reported to feed on coniferous hosts. Two spotted spider mite is a warm-season mite that will continue to be a problem the rest of the growing season. Treat populations early to avoid damage and overlapping generations that are difficult to control. I was surprised to find actively feeding spruce spider mites in Lawrence County last week. Spruce spider mite is a cool-season mite that typically feeds in late April through May. Damage is not often seen until the weather warms up, and the mite has diapaused for the summer. Look for inner needles and growth to have a grayish white appearance that makes the foliage look somewhat faded.
Eventually this leaf tissue will desiccate and may turn brown. Often you will see damage on previous season’s growth because the feeding has occurred before new growth. Large population levels of spruce spider mites can kill plants. Alberta spruce are especially susceptible to this pest. Close examination of infested needles will reveal stippling type damage, eggs and sometimes adults. But they can be hard to find. Again, treat this pest early and monitor for it in spring and fall. Maple mites were also found this week in Putnam County. This is an interesting mite species because it is the same genus as spruce spider mite. It seems to become active early in the year, but population levels keep climbing throughout the growing season, and it does not diapause like spruce spider mite. Look for a light amount of stippling on the top sides of leaves and small colonies of mites near the veins of infested leaves. As feeding continues, stippling will coalesce to form a white appearance across the entire leaf surface.
Maple petiole borer was found feeding on the new growth of red maples. Look for dieback of new growth on red maples. Often you will find that the new stem has been hollowed out by the larval feeding of this pest. If you get lucky, you can find the larva still feeding on the inside of the stem tissue. Large population levels can reduce the growth of newly planted trees, but typically this pest is not a major issue on red maple. Damage from boxwood psyllid was found in Putnam County. This pest actually feeds in late April and early May. It is too late to treat for this pest. Feeding activity from this pest causes leaf cupping. Damage from this pest is not a serious risk to the health of boxwoods. Another pest that can cause leaf deformity early in the season is the woolly birch aphid. You may see damage on your trees that appears as cupped or crinkled leaves. This is a result of early-season woolly birch aphid feeding. At this time of year, the new growth will be growing out ahead of the damage. Generally, this pest is not a serious threat to tree health.
Apple scab continues to develop on many varieties of apples. Large levels of infection may cause leaf drop as early as August. Cedar-hawthorn rust was found on the leaves of Winter King Hawthorn. Look for orange spots on infected leaves. There is another rust that occurs on the fruits and can also cause infection of small branches. This is the cedar-quince rust. It looks terrible when trees are heavily infested but does not often kill trees. The picture I have included in this week’s report shows some swelling on the outer stem tissue. This may be an early indication that both cedar-hawthorn and cedar-quince rust are occurring at the same time. Symptoms of needle cast were found on Scotch pine. Needle caste diseases are fungi that infect one complement of needles, while needle blights infect multiple years of needle growth. The symptoms of needle cast that develop are occurring from the previous year’s infection. The new growth of susceptible and infected trees should be protected with fungicide applications to prevent infection of new growth. It is a good idea to send a sample into the lab to determine which needle cast you have because the timing and type of fungicide you need to use may vary somewhat for each species.
One interesting cultural problem I encountered was little leaf syndrome on river birch. This is thought to be caused by a nickel deficiency. I do not have much experience with correcting this issue, but I occasionally encounter river birch trees with symptoms that could be nickel deficiency. If you think you have this issue, I recommend getting some leaf tissue and soil analysis performed to determine if it indeed the cause of your symptoms and how to best handle correcting the situation.
I’m not seeing a lot in the way of insect activity in east central Indiana. What I am seeing a lot of is bad cultivation, unfortunately mostly in garden centers. Whether it’s a lack of staff or knowledge, plants are sitting on the pavement in hot parking lots and just cooking and then the wind picks up, and material gets strewn all over so that even the plants that weren’t drought- stressed are getting knocked around and, in some cases, even getting knocked out of pots. This makes for a lot of extremely unattractive plants that will likely still be unsold at the end of the season.
The one bit of insect activity I did see was freshly hatched bagworm in Hamilton County. It’s a bit late in the season, but it’s been a fairly cool and slow spring up until now.
I thought I would include a couple of finds from around my home in Perry County. The first two photos are of a buck moth Hemileuca maia caterpillar, which is part of the giant silkworm family Saturniidae. If you see these spotted spiky guys, you should avoid touching them with your bare hands. You can get a painful sting, swelling, and redness from the spines along the body. The spiracles (openings to the respiratory system) have a pale brown color and are edged with black and can be seen in the side view of the caterpillar. Mature caterpillars are about 2.5 inches long.
The other photos are of a tomato hornworm Manducaquinquemaculata caterpillar and caterpillar damage to a tomato leaf. These caterpillars will feed on tomatoes, peppers, eggplant, and other plants in the Solanaceae family. This young instar caterpillar is about an inch long. They grow quickly and are 3-4 inches long at maturity. They can quickly defoliate your plants and cause heavy damage. The caterpillars blend with leaf color well and can be hard to see. Scout regularly (every 1-2 days) for these caterpillars. They can safely be removed with your bare hands and destroyed.
I have seen magnolia with holes in the leaves at a couple of different nurseries. I suspect this is yellow poplar weevil damage. The Buckeye Yard & Garden onLine has a great summary of this insect that they published a few years ago. This insect creates different forms of damage depending on the life stage and attacks yellow poplar, magnolia, and sassafras.
I am seeing a fair bit of spider mite on tropical plants. The low populations that often sneak in on the plant material are starting to boom as we encounter hotter temperatures.
