Southeastern U.S. Vegetable Crop Handbook - 2023 - 16

often used. By reducing the amount of water used and lowering
ambient temperatures, one can cause a " check " in plant growth
(a " slow down " ) to prepare plants for field setting. Never reduce
or limit fertilizer as a means to harden transplants because it
will often delay maturity. If ambient temperatures are too low,
chilling injury can result causing plant damage and delayed regrowth
after transplanting. Caution: Lowering air temperature on
some crops, such as cool season crops, might induce bolting.
DIF. Plant height can be held in check and hardening can be improved
by using a process that reduces or increases ambient temperatures
in the early morning over the course of several days.
Plants elongate most at daybreak. Raising the temperature before
daybreak (2 hours before) or lowering the temperature just after
daybreak (2 hours after) by 10°F will cause plants to be shorter
and more hardened. This process is called DIF, because you are
employing a difference in temperature. DIF can be positive or
negative, but positive DIF is more commonly used for hardening
transplants. Negative DIF can cause crop injury on cold sensitive
crops or bolting on cool season crops.
GRAFTING IN VEGETABLE CROPS
The phase-out of methyl bromide fumigation is driving the
search for alternative methods to manage soilborne pathogens
in vegetable crops. Although alternative pesticides and other
physical treatments are being tested and developed, grafting with
resistant rootstocks offers the best method to avoid soilborne
diseases. Grafting involves combining a desirable scion, which
is the fruit-bearing portion of a grafted plant, with a rootstock,
which provides resistance to various soilborne pathogens. The
scion is generally from a plant that produces highly desirable
fruit. However, grafting can also influence vegetative growth and
flowering, affect fruit ripening and fruit quality, enhance abiotic
stress resistance, and enhance yield especially under low temperature
conditions.
At present, most research is being conducted on grafting to
solanaecous and cucurbit plants. The primary motive for grafting
TABLE 6. VEGETABLE SEED SIZES
Crop
Asparagus
Beans:
small seeded lima
large seeded lima
snap
Beets
Broccoli
Brussels sprouts
Cabbage
Cantaloupes
Carrots
Cauliflower
Collards
Cucumbers
Eggplants
Endive, Escarole
Seeds/Unit Weight
13,000-20,000/lb
1,150-1,450/lb
440-550/lb
1,600-2,200/lb
24,000-26,000/lb
8,500-9,000/oz
8,500-9,000/oz
8,500-9,000/oz
16,000-19,000/lb
300,000-400,000/lb
8,900-10,000/oz
7,500-8,500/oz
15,000-16,000/lb
6,000-6,500/oz
22,000-26,000/oz
Crop
Kale
Kohlrabi
Leeks
Lettuce:
head
leaf
Mustard
Okra
Onions:
bulb
bunching
Parsnips
Parsley
Peas
Peppers
Pumpkins
Seeds/Unit Weight
7,500-8,900/oz
9,000/oz
170,000-180,000/lb
20,000-25,000/oz
25,000-31,000/oz
15,000-17,000/oz
8,000/lb
105,000-144,000/lb
180,000-200,000/lb
192,000/oz
240,000-288,000/lb
1,440-2,580/lb
4,000-4,700/oz
1,900-3,200/lb
Crop
Radishes
Rutabaga
Spinach
Squash:
summer
winter
Sweet corn:
normal and
sugary enhanced
supersweet (sh2)
Tomatoes:
fresh
processing
Turnip
Watermelons:
small seed
large seed
Seeds/Unit Weight
40,000-50,000/lb
150,000-192,000/lb
40,000-50,000/lb
3,500-4,800/lb
1,600-4,000/lb
1,800-2,500/lb
3,000-5,000/lb
10,000-11,400/oz
160,000-190,000/lb
150,000-200,000/lb
8,000-10,400/lb
3,200-4,800/lb
tomato and watermelon is to manage soilborne pests and pathogens,
when genetic or chemical approaches for management of
these diseases are not available. Grafting a susceptible scion onto a
resistant rootstock can provide a resistant cultivar without the need
to breed a resistant cultivar. Furthermore, grafting allows a rapid
response to new races of pathogens, and, in the short-term, provides
a less expensive and more flexible solution for controlling
soilborne diseases than by breeding new, resistant cultivars.
Grafted transplants are more expensive than non-grafted transplants
(as much as 4x) due to labor, material costs (grafting supplies,
seed costs of rootstock and scion), and specialized facilities required
to produce grafted plants. These specialized facilities include healing
chambers, grafting rooms, and trained personnel to produce and
care for these grafted transplants. Potential changes in fruit quality,
which occur with some rootstocks, must also be considered. Commercial
transplant producers offer grafting services and with improved
grafting techniques and mechanization, costs are decreasing.
Grafted transplants are available on the east and west coast.
The most current research and new developments in grafting
can be found at http://www.graftingvegetables.org. This
site contains the latest findings on grafting solanaecous (tomatoes,
peppers, eggplants, etc.) and cucurbit (watermelons, melons,
etc.) crops. You will find detailed tables listing research on
rootstocks and their specific attributes. The USDA-ARS has
released a watermelon rootstock (Carolina Strongback). This
rootstock has multiple sites for resistance to race 1 and 2 of Fusarium
and tolerance to root-knot nematode.
Grafting has become the predominately-practiced growing
method in Asia. Currently 95% of watermelons and Oriental
melons are grafted in Japan, Korea, and Taiwan. This is due to
their lack of land for rotation. Until recently, grafting had not
been considered a potential cultural practice in the US. However,
grafting is gaining popularity in the US due to increasing limited
land availability for rotation and the loss of soil fumigation
as a means for managing soilborne diseases. Currently grafted
transplants can cost three to four times that of a standard transplant.
Grafting presents an option, however, for soilborne pathogen
management for diseases such as Fusarium wilt, Monospo16
2023
Vegetable Crop Handbook for Southeastern United States
http://www.graftingvegetables.org
Southeastern U.S. Vegetable Crop Handbook - 2023

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