Ensuring crop production in specialty crops

Carole Curtis, Correspondent

Valders — Farmers and gardeners rely on wild bees and managed bees, like honey bees and blue orchard mason bees, for crop pollination and yields.

Strategies to support these pollinators of tree fruits, pumpkins, watermelons and other specialty tree fruits was presented by Theresa Pitts-Singer, USDA-ARS research entomologist, during the first  "Ensuring Crop Production In Specialty Crops", a Bee Health Webinar series being presented by eXtension Bee Health Community.

Pitts-Singer is part of the Integrated Crop Pollination Project (ICP Project), leading research on the use and management of blue orchard bees and alfalfa leaf-cutting bees, pollinators of fruit and nut trees and of alfalfa, respectively.

The ICP Project seeks to link the management of honey bees, alternative managed bees and wild bees with pesticide stewardship and horticultural practices. 

"We need to protect the bees that are doing the pollinations from any harmful effects of the pesticides that are necessary for crop production," Pitts-Singer explained, as well as employing practices such as no-till for ground nesting bees and bumblebees and making habitat enhancements for nesting and floral resources.

"Overall, the ICP system is to provide strategies to provide reliable and economical pollination of crops," Pitts-Singer said.

California has a big dog in the hunt, with nearly a million acres of almond trees requiring pollination. Almonds are the state's top agricultural export with the 2014 gross production value of over $6 billion, she said, and the largest exported U.S. specialty crop. 

Almonds are not particularly easy to grow, Pitts-Singer observed. The tasty, nutritious nuts are native to the Middle East, India and North Africa. In California, most native bees do not emerge until after the almonds bloom, which is very early in the spring, when no other blooms are available for pollinators.

Like many other crops, almond production hinges on the flowers receiving pollen from a tree of a different almond variety. Its work that bees are eminently suited for.

Every February, there is a mass migration of honey bees aboard trucks headed for California. A fleet of 1.8 million colonies will provide necessary pollination services, worth almost $15 billion, to the vast swaths of fragrant almond trees that burst into bloom for a few short weeks in early to mid-February.

It is, Pitts-Singer said, the world's largest pollination event. "It is actually quite spectacular and beautiful and it smells really nice," she noted.

The incoming hives, which are rented for about $200 each, are clustered into bee yards, where the honey bees are fed  sugar syrup and pollen patties until the almond blossoms unfurl. The substitute pollen is needed because the colonies need to grow their brood, not just sustain themselves, she noted.

Almond trees are grown in rows with the target variety flanked by rows of earlier and later blooming varieties in order to maximize pollination. Once the nuts mature, from mid-August to October depending on variety , they are mechanically shaken from the trees  and swept into aisle rows for mechanical harvest.

The ground is kept bare beneath the trees and between the rows of trees to facilitate the harvest.

Honey bees are excellent pollinators, but the challenges they face are many and intertwined, ranging from pests like varroa and tracheal mites to pesticide exposure and nutritional shortfalls in abundance and diversity. 

Blue orchard mason bees are considered even better at pollination, Pitts-Singer said. Nectar puddles in the base of a flower, while the stigma extends beyond the pollen anthers where it will rub on a bee's body as she heads in for the nectar.

Honey bees collect moistened pollen into pollen baskets on their hind legs, while blue orchard bees collect the pollen dry, mainly on their underbelly, where it is readily accessible for the flower's purposes.

Blue orchard bees also collect pollen and nectar on the same forage trip and tend to zip around randomly. "They will be just covered with pollen," Pitts-Singer said.

Honey bees, on the other hand, focus on either pollen or nectar collection and tend to work quite systematically through a tree.

Studies using a complementary system of one honey bee hive/400 female BOBs per acre is underway, compared to the conventional stocking rate of two honey bee hives per acre.

The on-going research shows a mix of bees provides better pollination. "We've seen sectors where the fruit set was much better when blue orchard bees were present," Pitts-Singer noted.

For one thing, the bees tend to drop loose pollen as they bustle around through the different varieties of trees. That mixture is picked up and further distributed by the honey bees in their systematic work through a tree.

Honey bees and blue orchard bees do not interact in a negative way. "Nobody really visits each other," Pitz-Singer said. "I think it's a really nice situation to have both at one time."

Blue orchard bee queens are stocked into an orchard by hanging boxes or laminated wood structures for them. Each queen will collect pollen and nectar for her brood, filling a tube in the nesting structure with a series of eggs and provisions separated  into individual compartments by a mud plug.

Interestingly, the eggs at the back of the tube will develop into females and the eggs closer to the front will develop into males, which are smaller and hatch first. The system not only keeps the more important females somewhat safer in case of nest predation, but the males will be on hand, ready for duty, when the females do emerge. 

Research on supplemental forage for honeybees is also underway in an effort to provide natural nutrition before and after the almond bloom. To date, it has shown that hives with access to forage have higher survival rates, Pitts-Singer said, and that the forage does not compete with almond pollination.

Some honey bee keepers are now contracting with growers for a reduced price if the grower provides forage for the bees.

Floral enhancement plots or rows to the side of the almond plots has been shown to be a benefit in studies conducted in 2015 and 2016. After bloom ended in March, Pitts-Singers'  team documented a continued increase in blue orchard bee nesting boxes populations close to the flower strips.

To help honey bees and other pollinators, farmers and growers can make use of "Best Management Practices", including a communication chain between the beekeeper, the farm manager, the pest-control advisor and the applicators. "Good communication will help to safeguard both the crop and the bees," Pitts-Singer pointed out.

Another measure is a "Pesticide Operators Agreement", a plan that outlines what pest control materials will be used, allowing the beekeeper to remove the bees in time to limit exposure to any substance that might be toxic to them, but necessary for the crop. 

"How To Reduce Bee Poisoning" is a publication that can be downloaded free from Oregon State University Extension. 

To protect bees, Pitts-Singer advises, do not spray during bloom and, whenever possible, do not spray when bees and pollen are present. Never spray directly on hives or nesting sites.

If spray is needed during bloom, make fungicide applications in the late afternoon or evening. Not only will the bees be back home in their hive or nesting tube, but since bees tend to strip the pollen during the day, there will not be that much left to contaminate.

IPC management strategies start with understanding the crop's needs, as well as the pollinator's preferences, behavior on flowers and susceptibility to issues, such as particular pesticides or lack of water. Be sure to provide any resources that are lacking for nesting and brood production.

"We need to develop not just IPM, integrated pest management, approaches,  but integrated pest and pollinator management (IPPM) approaches  and other practices that can safeguard bees and ensure they will be there for the next pollination event," Pitts-Singer said.

For more information, visit the Bee Health page at eXtension.org or http://articles.extension.org/bee_health.

Honey bees and other managed bees join wild bees in pollination efforts for the production and yields enjoyed by farmers, gardeners and growers.