Welcome to the Ultra Gro Agronomy Letter!
Hello and welcome to the July edition of the Ultra Gro Agronomy Letter.  This month we asked our agronomist, Robert Smith, to write a couple of timely articles for our growers. Nothing is timelier than a discussion about nut fill in pistachios and sunburn in grapes. And finally, how about a simple and brief refresher in regards to soil health and biology.  Thank you, Robert!
Nut Fill in Pistachios
By Robert Smith, Agronomist
California pistachios are renowned for their unique quality, flavor, and nutritional value. Achieving optimal nut fill, the crucial phase when pistachio nuts undergo significant growth and development, is of utmost importance to ensure high yield, split nuts, and quality. Filling is a two-step process - the ovary (the shell of the nut) grows first, then the kernel expands to fill it. Nut fill happens between July and August. It is always best to try to stay ahead of it on this agronomic event.

In some cases, pollination may occur, but because of weather conditions or nutrient issues, fertilization may not, resulting in a failure of the nuts to fill. Nutrition can play a role… boron/zinc deficiency can be a factor in some areas. Soil and leaf tissue testing is of the utmost importance. Boron leaf levels need to be at least 120 ppm. Other nutrients may also play a role. Tissue testing is the best way to monitor the nutrient status of the tree. 

Research has shown kernel filling is in a period of high nitrogen demand.  On-year trees took up 35 percent more nitrogen during kernel filling than off-year trees.  The nuts accounted for more than 90 percent of the accumulated nitrogen for the entire season. There can be yellowing of leaves adjacent to nut clusters in heavy bearing trees, but, I have not seen this yet.  This occurs even when tissue levels are considered adequate at 2.5%. It has been my experience, that in heavy bearing orchards with higher nitrogen levels, the yellowing does not occur. 

Potassium (K) uptake is also very high during kernel filling.  Research by Drs. David Zeng and Patrick Brown indicates adequate potassium supplies will significantly increase yield, split nut percentages, nut weight and reduced blank and stained nuts.

Another complication is drought stress. If there was insufficient available soil moisture before a period of high heat, that could also be a factor. Was irrigation adequate before the heat so that trees had adequate soil moisture during the period of heat? Irrigation can be a factor in failure to fill in mid-summer because the kernels fail to expand and fill the shell. 

Kernel filling requires lots of water, nitrogen, potassium, and boron. Average water use in July is 9.8 inches (55 gal/tree/day, 150 trees/ac).  August water use is 8.2 inches (50 gal/tree/day). You will need to adjust your schedule accordingly to the heat and your tree spacing. Deficit irrigation, nitrogen, potassium zinc or boron deficiency during kernel filling will dramatically reduce split nut percentages.

This year, kernel filling started in Kerman somewhat later than usual (about July 1). This varies by orchard and location.  This is why it is so important to monitor kernel fill in your own orchard. And while you are in kernel fill, it is also a good time to check soil moisture with an auger. Keep an eye on the temperatures and adjust your schedule accordingly. If you do not have any soil moisture monitoring equipment in the orchard, be sure to auger occasionally to check for moisture below two feet. From experience, deficit irrigation sneaks up on you, and before you know it, your trees are stressed and the kernel filling rate gets limited!

The standard method for sampling is to randomly collect 10 clusters of pistachio nuts from an area of the orchard, making sure north, south, west, and east sides of trees are represented in the sample. Nuts are cut lengthwise to see the developing green embryo. Each nut is rated from 0-5, 0 being no fill and 5 filled. After cutting and rating, count the nuts in each ratings pile and determine the percentage for each stage. Sampling a pistachio crop will give you some idea of the fruit set and crop development in your orchard. When you are finished cutting all the nuts, count the number in each category, and do the basic math to determine the percentages of each. Record your results to keep track of the development throughout the season. Performing this task at least every two weeks will tell you a great deal about what to expect at harvest, relative to maturity and crop load. Kernel fill is manageable and can take place at a faster pace later in the season provided trees are not water stressed or deficient in nutrients.

In conclusion, efficient irrigation, nutrient, and crop management during nut fill is critical for maximizing pistachio yield and quality. Achieving optimal nut fill in pistachio trees requires a comprehensive understanding of the crop's water needs, site-specific factors (including sound nutrient and agronomic principles), growers can enhance water use efficiency, nutrient use efficiency, minimize yield losses, and achieve sustainable pistachio production. Again, nut fill is manageable. Thank you.
Sunburn Protection in Grapes
by Robert Smith, Agronomist
“It’s always sunny in California.” If you think California is permanently 80 degrees and sunny everywhere, you're in for a surprise. As we all know, just when you'd expect the weather to be at its summery best, SJV temperatures can soar to 110oF or higher and coastal temps can become excessive also.  On so many levels this can be problematic, including the causation of sunburn in grapes — that results in a decline in berry quality, as well as a reduction in yield.

Sunburn is a physiological disorder that affects the visual and organoleptic properties of grapes. The appearance of brown and necrotic spots severely affects the commercial value of the fruit, and in extreme cases, significantly decreases yield. Depending on the severity of the damage and the driving factors, sunburn on grapes can be classified as sunburn browning (SB) or as sunburn necrosis (SN). Sunburn results from a combination of excessive photosynthetically active radiation (PAR) and UV radiation.

Hot weather, strong sunlight, and low humidity are a recipe for sunburn on grapes. On grape clusters, sunburn looks like a white, brown, or yellow blotch on the side of the cluster that is directly exposed to sunlight. This happens more often on the south- or west-facing sides of a grapevine. The blotch may be soft at first, but after a period, the affected area dries up and creates a berry that is hard on one side and partially mummified. Sunburned grapes do not ripen as well as normal grapes. Small amounts may not impact wine quality, but severely sunburned clusters should be dropped.

Sunburn can happen during any stage of fruit development if the conditions are right. While grapes need sun to ripen the fruit, too much direct sunlight beaming down on the fruit during low humidity can cause the fruit to burn – particularly after veraison, when berries begin to soften. 
No matter how careful you are, your grapevines will eventually get sunburned. And while it may not look like much, this seemingly harmless damage can hurt your grapes and reduce their overall yield.  One tool in the toolbox for growers is to use a solar protectant on your vines. When applied properly, growers can benefit from fruit protection, canopy health and overall, less heat stress.

Many of you have heard of our best-selling solar protectant, “Ultra Gro Crop Shield”.  We also have two other products, Game Changer and Cali-Kool. These products keep plants cooler, reduce stress, create longer “grow” hours during the day and give your grapes a chance to reach their full potential. And by the way, they are easily incorporated into your spray program and your Spray Rig guy will love you for the ease of mixing/handling/even application and the lack of plugging and wear and tear on the equipment. And just one more thing…it doesn’t break the bank…$25-$30 per acre will get you 30 days of protection.

Please call your UG Crop Advisor about these products and find which one is the right fit for your farming operation.  Thank you.
Soil Health and Biologicals
by Robert Smith, Agronomist
Soil health is the foundation of productive farming practices. Fertile soil and sustainable soil provide essential nutrients to plants. Soil health and soil quality are terms used interchangeably to describe soils that are not only fertile, but also possess beneficial physical and biological properties. What is soil quality?  “Soil quality” is the capacity of a specific kind of soil to function to sustain crop productivity, maintain or enhance water and air quality, and support human health and habitation (part of sustainability). The better the quality, the more it can do for us.

Soil fertility is the ability of a soil to provide the nutrients needed by crop plants to grow. The primary nutrients that plants take up from soil include: nitrogen, phosphorus, potassium, calcium, and magnesium. Frequently, we need to supplement soil nutrients by adding fertilizer, manure, or compost, for good crop growth. Plants take up many other nutrients from soil, as well.

Soil pH is another important aspect of soil fertility. pH is not a plant nutrient, but rather is a measure of the acidity of the soil. Most crops grow best when the agricultural soils have pH values of between 5.5 and 7.5. Soil pH has a profound effect on nutrient availability to crops. For the most part, a majority of essential plant nutrients enjoy their highest availability to crop plant species within the pH range of 6.0 to 6.5. This is the range in which plant roots can best absorb most nutrients from the soil. Failure to correct soil acidity can cause substantial yield losses and a decline in soil quality and soil health.

Organic matter is composed of plant residue, living and dead soil microorganisms, and substances produced through decomposition. Most soil in the San Joaquin Valley contains only a small proportion of organic matter (usually less than 1%).  However, this small amount plays a very large role in soil quality. Soil organic matter tends to improve soil fertility, soil structure, and soil biological activity. Organic matter is added to soils through cover crops, manure, compost, and crop rotation.

Healthy soils are teeming with living organisms: bacteria, fungi, insects, earthworms, etc. As these living things go through their life cycles, they perform many functions that help improve the quality of soil. Soil organisms decompose fresh organic matter such as crop residues and animal manures. In the process, they help soil particles stick together into stable aggregates. They also create humus, a form of organic matter that doesn't decompose further and helps soils hold water and nutrients. Soils with higher biological activity tend to have fewer plant disease organisms. Earthworms (often a sign of good soil health/quality) tunnel through soils, opening pathways for air and water to move into the soil. 

Inoculants are materials specifically used to enhance a soil’s biological component, such as microbial abundance and fungal/bacteria ratios. They can be used to help restore soil biology that has become depleted through conventional farming methods. This, when done right, can assist in nutrient uptake, reducing plant diseases and pests, and improving yields. It also shows great promise for increased carbon sequestration.

Without a doubt, microbial inoculants possess the capacity to enhance nutrient availability, uptake, and support the health of soil and plants to promote sustainable yield and plant growth. This piece of the fertility mystery has increasingly gained the attention of many agriculturalists and researchers in recent years.

Ultra Gro has a long history with biological inoculants and is a leader in their use in agricultural practices. In fact, we started propagating, growing and promoting microbes in 1985 (and that was way before they got cool!).  Please ask your UG Crop Advisor for more information.  Thank you.
Please call your Ultra Gro Crop Advisor if you have any questions.
Thank you!