David Doll8 CommentsJune 28, 2020Horticulture, Insects

Almond Gumming: When is it a problem?

An inquiry was received regarding almond gumming. The farmer observed clear gum exuding from multiple nuts in the fields. The concern was regarding the potential of a severe leaffooted plant bug infestation, and if an insecticide should be applied to reduce the damage. Generally, there are two types of damage that cause hull gumming: internal and external tissue damage. Internally, damage to the vascular tissues that surround the developing nut can cause gumming. This type of damage is often due to an enlarging nut that puts pressure on the hardened shell, leading to a disruption of the vascular bundles between the shell and the hull. Once the damage occurs, the exuded gum exits through the weakest point of the nut, which is often in line with the suture. This commonly occurs with varieties that have large kernels or in years with cooler than normal temperatures which provide conditions for larger kernel growth. It is not an issue as it does not affect harvest or kernel quality. External damage that causes gumming is more concerning. This damage can be caused by physical damage or by insects. Within orchard settings, knowing the weather history or location of the damage can lead to the diagnosis of the cause from abiotic issues (e.g. hail, equipment, etc). Damage from biotic causes is typically more random as it is usually caused by Hemiptera insects (e.g.true bugs), which include stink bugs and leaf-footed plant bugs. These types of insects have mouth parts that can pierce the hull and cause nut damage and loss. If the feeding is early enough in the season it can kill nuts, if after shell-hardening, feeding can still damage or discolor the kernel. The distinguishing characteristics to determine the difference is the location of the gumming. If occurring after shell hardening and in-line

Read More
David Doll4 CommentsMay 13, 2017Diseases, Horticulture

Almonds Exuding Clear Gum

Several calls about gummy nuts were received this week. Of concern are nuts that are oozing clear gum along the suture or side of the hull. There are many potential causes of clear gumming, which include bug damage, boron deficiency, and internal causes from an expanding kernel. Bug damage. Most people are aware of leaf footed plant bug damage. Feeding by this insect can kill the almond embryo when the insect inserts its needle-like feeding tube into the nut. This often leaves a small pin-prick hole which results in clear gum being exuded 3-10 days after feeding. Although the risk of the bug killing the embryo decreases after shell hardening, there can be some staining of the kernel. As the season progresses, feeding by plant bugs decrease, while stink bug feeding can increase. These insects do not have long enough mouth parts to feed on the kernel, but feed on the fruit instead. They often have several feeding points on a single nut. All of these may gum. Severe feeding by stink bugs may impact kernel quality, but the economic threshold of these insects is unknown. Boron deficiency. Too little boron can cause gumming. Usually a clear gum exudes out of the side of the nut or suture line. When cutting the nut open, the kernel is often discolored with copious amounts of gum. These nuts often drop from the tree, and if not, the gum can harden and misshape the kernels, impacting kernel quality at harvest. Another sign of deficiency is a low crop set. Tree boron status should be determined by hull analysis – which has been discussed previously.  This type of deficiency is common in areas that use clean surface water and have not applied any boron to the soil. Physiological- expanding kernels. Occasionally, almonds can gum for no apparent reason.

Read More
David Doll0 commentsApril 17, 2015Horticulture, Insects

Early Nut Split – Nut Drop or Bug Damage?

A few samples and farm calls have yielded nuts that are splitting pre-maturely. These nuts tend to be yellow in color and are often found dropping from the tree during high winds. Sometimes, the nuts have gum along the suture, or gum “specks” on the outside of the hull. These nuts could either be a “June Drop” as the tree is balancing the crop load or it could be kernel death caused by leaf-footed plant bug. The nuts dropped  could be the last dropping period within almonds. These nuts, when cut open, would be brown at the base of the nut, indicating the death of the connective tissue. Gum may exude from the suture of the hull. More importantly, there would be no noticeable holes through the hull or in the shell, although some degradation of the shell cells may occur. In contrast, Leaf-footed plant bug would have a pin hole through the hull. This hole would often extend through the shell and into the kernel, causing a darkened spot at the point of entry and a shriveling of the kernel. Gum may appear on the exterior of the hull where the bug entered its mouth parts, but does not always occur. Although gumming is usually immediate (if it occurs), nut yellowing and subsequent drop — based on research — occurs 14-23 days after the point of feeding/damage, variety dependent. Gumming is not as frequent on younger nuts. Knowing the cause of drop can provide information relevant to treatment decisions. If the drop is due to leaf footed plant bug, a treatment may be warranted. It is important, however, to determine if the bugs are still within the orchards. Since the nut drop is visible several weeks post feeding, the bugs may have moved out of the orchard and the

Read More
David Doll11 CommentsApril 26, 2014Horticulture, Insects

Almond Gumming – Insect Damage?

I have noticed gumming coming from the hulls of almonds in several orchards. The gumming is clear, and can come from multiple points on the nuts. I have also been seeing it more on ‘Nonpareil’ than ‘Monterey’ or ‘Fritz.’ Initially suspected to be leaffooted plant bug, I think these issues are caused by another insect or are physiological.

Read More
David Doll6 CommentsMay 10, 2013Insects

Leaffooted Plant Bug

I have been several calls in regards to leaffooted plant bug (Leptoglossus clypealis and L. occidentalis). Damage has been reported from various areas of the county, with significant damage observed within some blocks. Leaffoted plant bugs get their name from the leaflike features found on the back legs of the large nymphs and adults. Adults are about 1 inch long and have  a yellow or white zigzag line across their back. Females lay eggs in strands which are often found on the sides of almonds or pistachios.

Read More