Winter Mummy Nut Sampling in Almond: Additional Insights for Pest Management
Cameron Zuber, Orchard Crops Farm Advisor, Merced and Madera Counties
Jhalendra Rijal, Area IPM Advisor, Stanislaus, San Joaquin, and Merced Counties
When performing tasks in an orchard, it always helps to keep an eye out for other issues as these observations may help mitigate future problems. For example, winter sampling almonds nuts for navel orangeworm (NOW; Amyelois transitella) is a practice that should be done before the mummy sanitation effort as it informs mitigation practices for NOW in the upcoming growing season. As this involves breaking the hull and shell to see the kernel, other damage may be present that could indicate past or growing problems that need attention. While these observations cannot replace harvest sampling for insect damage, they can provide additional insight that may add to those sampling efforts.
To demonstrate, below are a few observations from a winter mummy nut sampling performed at an almond research site in Parlier, CA. For approximately 20 randomly selected trees, up to 15 nuts were collected from the canopy. While more nuts would have been preferred to be sampled, these were young trees, so few had more than 15 nuts remaining on the tree. Additionally, while nuts remaining on the soil surface can also be sampled for NOW, this site had few nuts present on the ground, so sampling nuts from the canopy was more representative.
Photos of NOW damage (left) and larvae (right) from mummy nut sampling in January.
While NOW was present, here we are discussing other potential problems that were also observed. One possible concern was the presence of kernels with hollowed-out meats leaving only the pellicle still present (i.e., the outer darker veining layer on almond kernels). Many types of insects that feed on organic matter, such as mealworms, darkling beetles, and earwigs, could cause this damage to the nuts on the ground. However, this type of damage is also indicative of ants. If there is a high prevalence of this damage both from this and a prior harvest sampling, then it can be assumed that pest ants are present in the orchard. Regardless, monitoring should be conducted in April for ants and ant activity.
Photos of almond kernels and removed hull and shells (bottom) and hollow kernel (top) from mummy nut sampling in January.
Withered and wrinkled kernels were also observed, which can indicate many possible causes, like insufficient watering and/or insect damage. A combination of observations can help narrow down a potential cause. For this orchard, the cause could be from leaffooted bug (Leptoglossus sp.) as these were observed during the growing season, showing how past observations may help inform future ones. However, there were also concerns with insufficient watering. Leaffooted bug is a sporadic pest, so the likelihood of it occurring again is uncertain. However, if the cause was insufficient irrigation and was prevalent enough to detrimentally affect harvest yields or grades, then it should be determined what caused this and when it occurred. Combining observation in this way can help narrow down to a potential cause. These winter observations should not be the main determining factor for management. Instead, these observations combined with harvest sampling and earlier in-season observations can help determine appropriate areas to focus on to increase overall orchard health and maximize yields and profits.
Photos of leaffooted bugs found in August of the previous calendar year in the orchard sampled in January.
Black and white speckling was also observed on kernels and on closer inspection, turned out to be striped black and white organisms. These were identified as a type of springtail (Collembola). While UC IPM for lettuce notes some species may damage plant seedling roots and leaves, springtails are prevalent in the environment and most likely are not a concern for an almond orchard. Even when planted, almond trees are established enough where springtails activity would not detrimentally affect the tree. There is also a possibility these springtails are beneficial as some species help with decomposing plant matter. The springtails observed in this orchard were not identified to a species at the time of writing but were most likely colonizing decaying plant matter and migrated from the soil to overwinter or mate in the trees.
Photos of almond kernels with striped black and white organisms (left) and enlarged photos of organisms (right) from mummy nut sampling in January. Organisms later identified as a type of springtail (Collembola).
While observations during winter mummy nut sampling efforts may be innocuous, these could provide insight on other things to keep an eye on to protect future crops, especially if these observations coincide with others from harvest sampling or earlier in the season. Some of the damage mentioned could affect the tolerance levels of your crop (e.g., defects), thus affecting the grade as well as yields. You need to know what you are looking at, determining the level of risk to your crop, and if it requires treatment or additional monitoring. Above are just some examples from one winter mummy nut sampling effort, but there are other opportunities for additional observations when performing tasks in an orchard. You just need to keep an eye open for anything that may provide that additional insight.
A helpful guide for seasonal pest management practices can be found here. If you would like more information on the leaffooted bug in almond, look here.
Special thanks to Kent Daane (UC Cooperative Extension Specialist) for identifying the springtails, Brent Holtz (Farm Advisor with UC Cooperative Extension in San Joaquin County) for his continued support of the research resulting from these observations, Phoebe Gordon (Orchard Crops Farm Advisor for Madera and Merced counties) for reviewing the article, and Julio Perez (Biological Science Technician with USDA-ARS) and Omar Abulghanam (Biological Science Technician with USDA-ARS and Student with CSU-Fresno) for first observing and reporting the springtails’ presence in this orchard.