Southeastern U.S. Vegetable Crop Handbook - 2022 - 37

complicated to do than cleft grafting because it only requires a
single, straight cut on both the rootstock and the scion. In addition,
because fewer intricate cuts are involved, this technique
can be used on very small seedlings. Grafting can be performed
at various stages of seedling growth. Grafting at the 2-3 true
leaf stage is common. With both cleft and tube grafting, the
newly grafted plants must be protected from drying out until the
graft union is healed. This usually involves covering the plants
with a plastic cover or protecting them in some type of healing
chamber where temperature and humidity can be regulated.
Some method should be employed to reduce light intensity to
the grafted plants for several days after the procedure. It is critical
to increase the humidity in the chamber to near 100% for
the first two days. Humidity must then be reduced incrementally
over the next five days to prohibit the formation of adventitious
roots from the scion and to provide time for the graft union to
heal. Tomato grafts heal quickly and the seedlings can be acclimated
back into the greenhouse after 4-5 days.
With both cleft and tube grafting, it is important that the
diameter of the cut ends (of the scion and the rootstock) match
up perfectly. If the diameter does not match, the graft may not
heal properly, if at all. Rootstock cultivars tend to have different
growth habits than scion cultivars so it is important to grow a
small amount of rootstock and scion seed at first to determine
their growth rate relative to each other. Rootstock cultivars tend
to be more vigorous than scion cultivars. Another critical factor
is to cut rootstock seedlings below the cotyledons. If the cotyledons
are left, they will generate suckers that will compete with
the scion and requiring pruning. For step-by-step instructions,
go to http://graftvegetables.org/.
DISEASE CONTROL IN PLANT BEDS
For the best control of all soil-borne diseases, use a good commercial
plant-growing mix. If this is not possible, use one of the
following procedures:
Preplant. The only practice that ensures complete sterilization
of soil is the use of steam. When steam is used, a temperature of
180°F must be maintained throughout the entire mass of soil for
30 minutes.
Further information on sanitizing equipment, storage houses,
produce and water can be found in Table 3-51.
Seed Treatment. Seed treatment is important to control seedborne
diseases. Use of untreated seed could lead to diseases
in the plant bed which could reduce plant stands or result in
diseased transplants and potential crop failure. See sections
on SEED TREATMENTS for detailed information on how to
properly treat seeds and for materials labeled for use as seed
treatments.
Postplant. Damping-off and foliar diseases can be a problem
in plant beds. To prevent these diseases, it may be necessary to
apply fungicide sprays especially as plants become crowded in
plant beds. Refer to label clear ance before use. The use of sphagnum
moss as a top dressing will reduce damping-off because it
keeps the surface dry. See the section on GREENHOUSE VEGETABLE
CROP DISEASE CONTROL.
2022 Vegetable Crop Handbook for Southeastern United States
SEED STORAGE AND HANDLING
Both high temperature and relative humidity will reduce seed
germination and vigor of stored seed. Do not store seed in areas
that have a combined temperature and humidity value greater
than 100 [e.g., 50°F + 50% relative humidity]. In addition,
primed seed does not store well after shipment to the buyer.
Therefore, if you do not use all the primed seed ordered in the
same season, have the seed tested before planting in subsequent
seasons.
Corn, pea, and bean seed are especially susceptible to mechanical
damage due to rough handling. Bags of these seed
should not be dropped or thrown because the seed coats can
crack and seed embryos can be damaged, resulting in a nonviable
seed. When treating seed with a fungicide, inoculum, or other
chemical, use only gentle agitation to avoid seed damage.
PLANT POPULATIONS
For vegetable seed sizes and plant populations see Tables 6 and
7.
IRRIGATION
Basic Principles. The most common use of irrigation in vegetable
production is to supply the crop water demand. However,
irrigation events can also be used to modify the crop microclimate
(i.e., frost protection), control weeds, leach salts, or deliver
fertilizer and chemicals to the growing crops. To supply the crop
water demand, maintaining proper soil moisture levels is important
to maximize the productivity of vegetable crops. Plant
stress caused by too much or too little soil moisture can lead to
decreased size and weight of individual fruit and to defects such
as: toughness; strong flavor; poor tip fill and pod fill; cracking;
blossom-end rot; and misshapen fruit.
Once irrigating according to the soil water status, it is imperative
for growers to maintain the soil moisture level near field
capacity at all times during the growing season. Field capacity
is the maximum water the soil can hold. When the soil moisture
status/content/tension is at field capacity it means soil water
availability is ideal for crop development. However, to maintain
field capacity always requires a strategic scheduling of irrigation
events, so the irrigation system is capable of make uniform, frequent,
and precisely timed applications. Commonly, more than
one irrigation cycle per day may be needed to maintain field
capacity. This is particularly true for fast growing crops grown
in soils with little water holding capacity, such as sandy loams.
Even relatively short periods of inadequate soil moisture can adversely
affect many crops.
Another important aspect to take into consideration to determine
irrigation events using the soil water status is the soil type.
Different soil types have different moisture holding capacities
and the use of soil moisture sensors is essential to ensure proper
water availability. Soil moisture sensors are the most common
technology used to monitoring the soil water availability for
plants and recent research indicates that maintaining soil moisture
levels in a narrow range, just slightly below field capacity
37
http://www.graftvegetables.org/
Southeastern U.S. Vegetable Crop Handbook - 2022

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