Rel,.atlonship of Temperature and Date of Planting to Head Formation
 of Several Varieties and Strains of Crisp-Head Lettuce

 19 8

 James C. Hoffman


 Some progress has been made in the production of crisp-head lettuce in the
Everglades area of Florida. The problems are many, but disease resistance and con-
trol are at present the limiting factors in the production of lettuce when grown in
southern Florida.

 Varieties and strains of the crisp-head type that will head under adverse
climatic conditions is a second factor of great importance. A rapid rate of growth
is one of the determining factors in the formation of compact-hard heads and is
generally correlated with the available nutrients and water, with temperature being
Ian important factor.

 Thirteen varieties and strains of lettuce were planted at 6 different dates as
listed in Table 2. Several strains of Great Lakes were included in the tests as
the variety is generally considered quite variable under different climatic condi-
tions, and even the many strains are not fixed types*

 Each seed stock was planted in a randomized block layout with 5 replications.
Each replicate consists of 2 rows, 25 feet in length. The plots were located on
well mature sawgrass peat with a pH of 6.00.

 The seed were planted on open type beds prepared about 6 inches in height.
Fertilizer was applied to the beds broadcast 10 days before planting at the rate
of 500 pounds of 0-8-24, 50 pounds manganese sulfate, 25 pounds copper sulfate; 25
pounds zinc sulfate and 10 pounds borax per acre. Spergon treated seed were covered
1/2 inch in depth with soil and the beds were protected with cloth until the seed*
Lings emerged.

 All rows were spaced 24 inches apart and the lettuce transplanted on level
ground 12 inches apart in the row.

 Fertilizer was applied to all plantings at the rate of 500 pounds of the same
analysis as used on the seedbeds. The fertilizer application was placed in 2 bands
3 inches on each side of the plant row and 2 inches in depth.

 To control wireworms on the 5th and 6th plantings, 8 pounds of 40 percent
chlordane was applied per acre as a side dressing. The chlordane was mixed with
peat at the ratio of 1:19, This chlordane peat mixture was applied to the 5th
planting 1 month after the lettuce was transplanted. To the 6th planting the mix-
ture was added to the fertilizer and distributed at the time of transplanting.
This method of wireworm control appeared very adequate,