Commercial Production of Pickling &
Slicing Cucumbers in North Carolina

Pollination of Pickling and Slicing Cucumbers

The process of transferring pollen from the male flower to the female flower is called pollination. It is essential for cucumber fruit development and deserves the full attention of the grower. Pollination is done mostly by bees visiting open flowers. A limited amount of pollination is done by other insects.

Honey bees are excellent pollinators. When they extend their tongues into male flowers to eat the nectar, pollen sticks to their hairy bodies. When the bee visits a female flower, some of that pollen touches the sticky stigma allowing pollination to occur. Honey bees also serve as excellent pollinators because their numbers can be controlled and they can be forced to work cucumbers, which have less nectar than other plants. The honey bee, unlike many other pollinating insects, gathers pollen and nectar from one type of plant (for example, only cucumbers) at a time.

Honey bees may not be needed in small fields (3 acres or less) that are adjacent to natural, undisturbed areas where plenty of wild bees nest. In these cases, bumble bees can be sufficient pollinators. Bumble bees are much more efficient pollinators than honey bees because fewer visits to the flower are required for pollination (Stanghellini et al. 1997). Large fields, or small fields that are not near natural areas, will probably require the use of honey bees for good pollination and high yields. Yield increases of 25% to 30% are common when honey bees are introduced into the field. An indication of adequate bee activity in a field is being able to hear the bees buzzing.

Generally, one strong hive of honey bees (25,000 to 30,000 bees) is recommended per acre for hand-harvested cucumbers. For higher plant populations (as in machine harvest), three to four hives per acre may be required. An average of one bee per plant is recommended. Cucumbers require large numbers of honey bees for adequate pollination because the female flower is only receptive for part of a day (morning and early afternoon). Each flower requires an average of 11 bee visits to produce a well-shaped cucumber. However, the bees will often visit the flowers more frequently. Occasionally, the number of bee visits is not sufficient for adequate pollination resulting in misshapen fruit (Figure 6).

To obtain maximum benefit from honey bees, proper management is critical. Consider the following suggestions:

1. Place the hives evenly around the edge of the field in groups of four hives or less. The hives should be spaced so that no place in the cucumber field is farther than 300 feet away from a hive.
2. Do not place hives in the field until cucumber flowers are present for three to four days.
3. Position the hives so that they face east and are shaded during mid-day and afternoon (Figure 7).
   Fig. 7. Beehives are placed adjacent to cucumber field
   and in shade to reduce midday heat.

   

    

4. Locate hives upwind of any pesticide application when possible.
5. Avoid placing hives in high-traffic areas.
6. Keep a container of clean water near the hive if another source of water is not near. Place some floating sticks or similar objects in the water so that the bees can land while they are drinking their water.
7. Be careful when applying insecticides to cucumbers because insecticides can kill bees. Apply only when necessary and when bee activity is low, in the late afternoon (at least after 2 p.m.) or evening if possible. Use formulations that minimize drift downwind of the bee hives.
8. Destroy or mow nearby flowering weeds that attract bees away from the field. Honeysuckle, clovers, and buckwheat create competition for the attention of pollinating bees.
9. Do not remove hives from the field until sufficient pollination has occurred. For once-over harvesting, 6 to 10 days of good bee weather (at least 70°F and minimal rainfall) is usually sufficient. Bees should remain in the field for hand harvest until two to three days before the last harvest.
10. Irrigate either early in the morning (before 8 a.m.) or delay until late afternoon or evening (at least 4 p.m.) to minimize the impact on bee activity and optimize fruit set. Bee visits can be reduced 80% when overhead irrigation occurs during times of high bee activity.

Contact your beekeeper well in advance so that adequate hives can be placed in the field at the right time for good pollination. Rental fees will vary; however, costs are usually less in spring than summer or fall because less pesticides are used during crop production.

Sugar or pheromone-based bee attractants are not effective for increased bee activity, better fruit quality, or increased yields (Schultheis et al. 1994). Bee hive placement in fields is the most reliable method of meeting crop pollination needs.

Irrigation of Pickling and Slicing Cucumbers

Cucumbers have a high water requirement and are very susceptible to water stress. Lack of water can result in reduced fruit quality and yields. Under normal conditions, the crop needs approximately 1 inch of water per week. When the crop is fruiting especially during periods of hot, dry weather, under windy conditions, or both up to 2 inches of water per week may be required by the crop.

Uniform soil moisture is especially critical during plant establishment. If the soil lacks good moisture at planting, ¹/₂ to ³/ ₄ inches of water should be applied to provide uniform moisture. This will result in more uniform, complete plant stands which in turn result in improved, concentrated fruit yields and efficient use of machinery and labor. If soil is dry and requires irrigation after seeding, reduce water droplet size by increasing delivery pressure. Large water droplets often lead to soil crusting, which can inhibit plant emergence. Soil crusting leads to reduced stands that are not uniform. Obtaining a complete, uniform stand is especially critical because plant and fruit development must be uniform throughout the entire growing season to maximize yield.

If cucumbers do not receive sufficient rain or irrigation, fruit quality and yield are reduced and symptoms are indistinguishable from poor pollination (Plate 5). Irrigation can increase yield by more than 50% in years of medium to low rainfall. Irrigation rate will depend on soil type but applications should not exceed 0.40 inch per hour for sandy soils, 0.30 inch per hour for loamy soils, and 0.20 inch per hour for clay soils. Higher rates will waste water and cause soil erosion and fertilizer runoff.

Plasticulture for Hand-harvested Pickling and Slicing Cucumbers

Use of plasticulture (black plastic and drip irrigation) is a viable option for producing cucumbers, especially slicing cucumbers. The economics of using plastic mulch for producing only one crop of pickling cucumbers is questionable. When double cropping, however, it may serve well as a second crop option (Plate 6). Use of plastic mulch with drip irrigation tape increases production cost, but offers certain advantages such as increased yield, weed control, better quality, and earliness. A crop produced with plasticulture can increase yields two-fold over a crop produced with good growing practices without plastic but with irrigation, and yields nearly five times more than an average North Carolina crop with limited or no irrigation (Sanders et al. 1995). A more consistent yield can be expected with plasticulture because moisture and fertilizer can be applied whenever needed. In addition, plastic helps control many weeds, improves fruit quality, and reduces belly rot (see Disease Management section) by reducing fruit contact with the soil. It can also result in 7 to 10 days earlier production, permits more efficient fertilizer retention and placement, and reduces water logging by draining excess water away from plants. In high-organic-matter soils, plastic should be considered to reduce soil adhering to fruits. It will also help reduce fruit rots (Jones 1961).

As mentioned earlier, soil preparation is a very important part of growing a productive cucumber crop. This also holds true with plasticulture. Failure in the plasticulture system can often be traced back to poor soil and bed preparation. Soil must contain adequate moisture, and be loose and free from trash (rocks, plant debris, etc.) so that plastic and soil are in direct contact and form a smooth bed. The plastic mulch should be laid tight to form a tight bed. The bed height should be near 6 inches with the center of the bed about 1¹ /₂ inches higher than the sides of the bed so that rain will not accumulate on the plastic. There are several bed presses available that can be used to form close contact between the plastic mulch and the soil surface.

When growing on plastic mulch, plant populations of 20,000 to 30,000 plants per acre are suggested (Table 5). Double rows should be planted approximately 6 to 8 inches to each side of the centrally placed drip tape. In-row spacing should be 10 to 14 inches between plants. Avoid having more than one plant per hole as multiple plants reduce yields.

With drip irrigation, micronutrients, phosphorus, and approximately 30% of the nitrogen and potassium should be incorporated into the bed before covering it with plastic. Commonly used nitrogen fertilizer sources for pre-bedding application include ammonium nitrate, calcium nitrate, and potassium nitrate. For potassium, common sources include potassium chloride, potassium nitrate, and potassium sulfate. Potassium sulfate is a good choice for sandy soils that are deficient or low in sulfur. Superphosphate (normal and triple) is a good source of phosphorus.

The remainder of the nitrogen and potassium should be applied through the drip system to coincide with plant growth and development through the season. Fertilizer applied with water through the drip tube (fertigation) should be high quality greenhouse grade so that the drip tube does not become clogged. Calcium nitrate and potassium nitrate are the most common forms of nitrogen and potassium fertilizer used for fertigation. However, ammonium nitrate, sodium nitrate, urea, diammonium phosphate, and nitrate of soda potash are also used.

Fertigation can be automated for a wide range of frequency from daily to biweekly. There is debate between researchers about the best frequency for fertigation; however, more frequent application could be closer to plant needs. Beginning when four true leaves have developed, tissue samples should be taken and analyzed every two weeks to determine the nutrient status of the crop. Results of that analysis should be compared with the foliar nutrient sufficiency range for cucumbers (Table 3) and fertilizer adjustments made accordingly. A total of three tissue samples during a production season should be sufficient.

Table 9. Suggested fertigation schedule for cucumber (N:K; 1:2)

Days after planting	Daily nitrogen	Daily potash	Seasonal nitrogen	Seasonal potash
	———————— lb/acre ————————
(preplant)			45.0	45.0
0–7	0.9	1.8	31.3	62.6
8–14	0.9	1.8	37.6	75.2
15–21	1.3	2.6	47.7	83.4
22–28	1.3	2.6	57.8	101.6
29–35	1.5	3.0	68.3	122.6
36–42	1.5	3.0	78.8	143.6
43–49	1.5	3.0	89.3	164.6
50–56	1.5	3.0	99.8	175.6
57–63	1.5	3.0	110.3	196.6
64–70	0.7	1.4	115.2	206.4
71–77	0.7	1.4	120.1	216.6

Note: N=nitrogen, K=potassium as K₂O
Adapted from Sanders et al. 1995.

In Table 9, a fertigation schedule is given as a starting point. This may need to be modified according to crop status, soil type, weather, etc. Other fertigation schedules have worked successfully in North Carolina. The University of Florida fertigation schedule recommends a 1:1 ratio of N and K₂O over a 10-week period (Table 10). In addition to 24 pounds of preplant fertilizer, a total of 120 pounds of N and K₂O are applied through the drip tape during the season. For more specific information on use of plasticulture in vegetable production, refer to bulletin AG-489, "Plasticulture for Commercial Vegetables."

Table 10. Alternative fertigation schedule for cucumber (N:K; 1:1), option from Florida.

Days after planting	Daily nitrogen	Daily potash	Seasonal nitrogen	Seasonal potash
	———————— lb/acre ————————
(preplant)			24.0	24.0
0–7	1.0	1.0	31.0	31.0
8–14	1.5	1.5	41.5	41.5
15–21	1.5	1.5	52.0	52.0
22–28	2.0	2.0	66.0	66.0
29–35	2.0	2.0	80.0	80.0
36–42	2.0	2.0	94.0	94.0
43–49	2.0	2.0	108.0	108.0
50–56	2.0	2.0	122.0	122.0
57–63	2.0	2.0	136.0	136.0
64–70	1.5	1.5	150.0	150.0

Note: N=nitrogen, K=potassium as K₂O
Adapted from Hochmuth and Clark 1991.