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POLLINATION AND POLLINATORS

(Nicholas Calderone nwc4@cornell.edu, Entomology, Ithaca)

The honey bee-Apis mellifera - Solitary bees and the bumblebees are often the best pollinators for many crops. However, many modern agricultural practices, such as the use of large monocultures and an increasing variety and quantity of herbicides and pesticides, have reduced or eliminated many wild pollinator populations. High-density plantings also bring about a demand for large numbers of pollinators, and native bees often cannot reach the interiors of large fields or orchards. Consequently, growers often find that natural populations of pollinating insects are insufficient to ensure adequate pollination. The honey bee is widely used to supplement inadequate populations of native pollinators.

How many colonies do I need? - This depends, in part, on what else is available within the bees' foraging range, which extends about 2.5 miles from the colony and covers an area of about 12,500 acres. Your crop must compete with everything else within that area. For that reason, a general recommendation of one strong colony per acre for most crops makes a good starting point from which you can make adjustments based on personal experience. Below, I outline a few cases where more detailed information is available.

New York apple growers have traditionally used about one colony per three acres. This number may have been adequate in small orchards visited by feral honey bees and by solitary bees and bumble bees from adjacent hedgerows and woods. However, feral honey-bee populations have been greatly reduced in recent years, and modern agricultural practices have eliminated many natural nesting sites for solitary bees and bumble bees. In addition, the flight range of solitary bees is not generally sufficient to ensure coverage of the center portions of large plantings. Growers with large blocks of apples and other tree fruits may wish to increase the number of colonies to one per acre. If your fruit set has been lower than expected, or your fruits are misshapen, you probably need to use more bees. Remember! If your fruit set is too high, you can always thin, but if it is too low, you are just out of luck. Apples are self-incompatible and require the presence of a pollinizer cultivar for fertilization. Honey bees should be moved into apple orchards when 5-10% of the king blossoms are open.

Some crops have special requirements. Red Delicious apples have flower structures that are different from most other varieties. The anthers are widespread, and bees learn to insert their mouthparts between the anthers to obtain nectar. This results in less contact with the sexual organs and, consequently, less pollination. It takes time for bees to learn to obtain nectar this way. To counter this problem, the number of colonies in the orchard can be increased so there are more naive bees present. Two colonies per acre may be needed in large stands of red delicious apples.

Pollination of pears will probably always be a problem because pear nectar contains only about 15% sugar compared to 40% for apples, dandelions, and yellow rocket. The answer is to move the bees into the center of the pear block when the pears are at 30%-50% bloom. It will take some time for the bees to discover better sources farther away, and in that time, the pears may be adequately pollinated. An alternative is to use more colonies per acre, which will increase the number of bees foraging within the orchard. Pears can be completely or partially self-sterile, depending on the conditions under which they are grown. Where pears do not set a parthenocarpic crop, you can interplant cross-compatible cultivars.

Cherry blossoms should be pollinated as soon after they open as possible. Move bees into sweet cherries the day before bloom. A considerable reduction in yield can result from being late with bees on sweet cherries. Sweet cherry cultivars will not set fruit with their own pollen and require a compatible pollinizer cultivar for good crops. Additionally, many cultivars of sweet cherries are inter-incompatible with each other. Move honey bees into sour cherries the day after the blossoms begin to open because they have less attractive nectar than that of sweet cherries. Moving the bees in right after bloom begins provides the bees with a greater incentive for working close to the colony for a longer time. Sour cherry cultivars range from self-fertile to self-incompatible. In general, sour cherries set a good crop if there are sufficient numbers of pollinators present. Two colonies per acre may be required because cherries require a high fruit set for a commercially viable crop and because they bloom early in the season when the weather is often unfavorable for foraging.

Getting the most from the bees - There are a number of things you can do to maximize the benefits from honey bee colonies. There are also a number of steps you can take to guard against damaging the bees while on location. Remember! If the colonies are damaged while on location, not only do you receive less pollination, but the beekeeper will eventually have to increase rental fees to make up for the loss.

Moving bees - It is generally best to move bees onto location after the flowers on your crop have begun to open. A rule of thumb is at 10-20% bloom. However, some crops, as mentioned above, have special requirements. Some growers rotate bees between distant fields every few days in an effort to keep the bees close to their hive. While this may seem to make sense in view of the bees foraging behavior, it does not take into account the loss of foragers that occurs with each move. Therefore, the net gain associated with this practice is unclear.

Pesticides and bees - Pesticides can kill the bees you have rented, causing serious financial problems for the beekeeper who ends up with damaged or dead colonies. Pesticides may also result in liability problems for the grower. Remember! The less pesticide used the better. If a pest emergency arises, contact your beekeeper, discuss the situation, and arrive at an agreement on fair compensation in the event that there is damage to the bees. Large numbers of dead bees accumulating rapidly in front of one or more colonies usually indicates pesticide damage. If you notice this symptom at anytime, contact the beekeeper immediately.

There are a number of steps you can take to reduce the potential for damage from pesticides. Never apply pesticides to crops in bloom. Remove flowering weeds from orchard cover crops and field edges. Follow an IPM program to reduce the number of sprays and use low-hazard materials whenever there is an option. Select low-hazard application methods. Systemic pesticides are better than sprays, and fine sprays are better than course ones. Use low-hazard formulations. In order of greatest to least danger to bees are dusts, wettable powders and emulsifiable concentrates. Do not spray when the wind is greater than 5 mph and use spray adjuvants to reduce drift. The best time to apply a pesticide is at dusk, when there are few bees in the field and when the pesticide will have time to break down before the next day. Lastly, dispose of pesticide containers properly.

Water - Provide a source of fresh water nearby for the bees. Without water, the bees will be unable to regulate the temperature inside the hive and may die. Bees will abandon pollen foraging to search for water if they are overheated and, consequently, they will be of less value for pollination. This recommendation is especially important in areas where the weather is hot, the air is dry, and the sun is shining. A large, galvanized tub makes a good watering station, but it must be equipped with lathe strips or a floating screen on which the bees can land while they are collecting water, otherwise, they will drown.

Placement of colonies - Pay attention to the placement of colonies. When possible, place colonies out of sight of the public and away from roads to minimize liability problems and vandalism. News reports of so-called "killer bees" have made many people perceive all bees as a threat, even at a distance. The old adage, "out of sight out of mind", works well when it comes to bees. Posting your orchards or fields with warning signs may reduce claims of negligence in the event of a stinging incident.

The placement of colonies in a field or orchard can affect their efficiency as pollinators. Distribute colonies in groups of 4-6 in orchards. Many commercial beekeepers have 'palletized' their bees into groups of 4-6. Do not attempt to separate these colonies. You can place colonies in groups of 10-20 to take advantage of a limited number of sites with good sun. Be sure to place colonies near the pollinizer variety if one is present. In large fields, place colonies in groups spaced 500 feet apart. The number of colonies per group is determined by the number of colonies per acre desired. Hive entrances should face south and be in full sun whenever possible. In addition, colonies should be elevated at least 4 inches off the ground, preferably more. This will help warm the colonies in the morning and get the bees flying earlier.

Bear fences - Spring is one of the peak times for bear damage to bees. If you are in an area with known bear activity, erect a temporary electric bear fence to protect the bees, or inform the beekeeper of potential bear problems so he can take preventive action.

Other factors affecting fruit set - Pollination is only one factor that affects fruit set. Some crops may fail to set fruit if the temperature is too high during bloom. Inclement weather may prevent pollinators from visiting your crops. Nutritional factors such as boron levels also affect fruit set. Be sure to explore all aspects of your crop system to ensure that you have done everything possible to encourage a good fruit set.

5/3 Chemical News