Nebraska's Forest Health Report for September 2026

The panhandle of Nebraska has had no relief from drought this year making it extremely difficult for trees. As we transition into the fall months, we hope that this pattern will change and moisture will make its way to those counties that need it most. Continue to water in periods of drought even in the winter when conditions are favorable to do so.

Flowering Fruit Trees in September?

Photo courtesy of Lauren Keefe

The apple tree, located in Alliance (Box Butte County), has flowered in September. This is a good example of how extreme environmental conditions, like continued exceptional drought, can play a role in tree performance and health.
Fruit trees require a lot in order to set buds, flower and produce fruit. Adequate sunlight, soil nutrients, proper pruning and water throughout the year plus enough "chilling" hours in dormancy is just a sample of what is needed for flowering in the spring. Flower buds are also more sensitive to early or last frosts.

Chilling hours are the number of hours the tree sits in dormancy between 32-45 degrees. These hours do not have to be consecutive but depending on the variety, apple trees need on average 500-1000 chilling hours before the tree can "wake up" properly and buds break dormancy. This chilling hour average could be more of less geographically. To make it even more complex, any hours with temperatures below 32 degrees do not count and any hours above 45 degrees gets subtracted by an amount that is debated across many platforms.

The panhandle of Nebraska has been in exceptional drought for so long and factoring in all that needs considered when dealing with fruit production, it's no wonder this tree is confused.

Moth larva on bur oak, Omaha, NE | Photo courtesy of Jennifer Morris

Polyphemus Moth

The Polyphemus moth (Antheraea polyphemus) is a giant silkworm moth sharing the same family as the luna moth. The Polyphemus caterpillar (pictured above) can grow up to 4 inches in length before making its cocoon in August/September, where it will spend the winter months as a pupa. The adult moths emerge in the late spring - early summer, and 2 broods are possible in Nebraska.

Adults do not have functioning mouth parts and only survive on stored fat reserves up to 15 days. The adults only job is reproduction. The adult moth can have a wingspan reaching 3-5 inches and its most notable trait are the patterns on the hindwings and forewings that look like eyes.

Larva feed on leaf tissue of trees, preferring oaks, maples and elms but feed on many hosts in Nebraska. Typically, Polyphemus caterpillars do not harm trees although they can be ferocious eaters at the later stages of their life cycle before cocoon development (as shown on the oak below).

Young bur oak defoliated by young Polyphemus moth | Photo courtesy of Jennifer Morris

Polyphemus Adult | Photo courtesy of Steve Katovich

Oak Bracket Fungus

Oak Bracket at base of oak tree in Fillmore County | Photo courtesy of Kim Slezak

Inonotus dryadeus, also known as weeping conk or oak bracket, is a common rot fungus of oak trees, other hardwoods like ash or maple and even some conifers. This rot attacks roots and lower trunk wood of its host causing structural integrity loss. The infected host may show signs of decline like leaf loss and branch die back. An infected tree can also look healthy with no signs of decay and then fall over in high winds. This can make it harder to determine the extent of rot, making infected trees unpredictable.

Fungal bodies can be easily identifiable by their shape and color along with pores that seep an amber colored liquid (how it gets the name weeping conk). Each year, the fungus produces these round or oval conks at the rot site whose color starts as a yellowish orange on the top and white on the underside. Weeping starts in the spring and early summer. By the end of the season, the conks have dried out, cracked and turned an orange/brown.

There is no cure for oak bracket. If fungal bodies are present, use a mallet to sound for hollow spots (a sign of decay), or contact NFS, Extension or a trusted arborist in your area for further inspection as these types of infections are unpredictable and may be a hazard.

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