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V e g e t a r i a n  N e w s l e t t e r
  
 A Vegetable Crops Extension Publication
    Vegetarian 03-10  grnbullet.gif (839 bytes) October 2003

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Effect of Metam Potassium Applied via Drip Irrigation on the Control of Purple Nutsedge (Cyperus rotundus L) on Four Widths of Polyethylene Covered Beds

The use of polyethylene mulch, drip irrigation, and the soil fumigant methyl bromide are all important components of successful cultural practices used by vegetable producers in North Florida. The US Congress legislated the phase-out of methyl bromide for this use by 2005.  Nutsedge is a common weed in the Suwannee Valley region of North Florida that has been adequately controlled in field plasticulture systems by using methyl bromide. This trial was conducted to evaluate metam potassium as an alternative soil fumigant for the control of nutsedge when applied via two drip tapes per bed using various bed widths.

Materials and Methods

Plots were established in the spring of 2003 on a Lakeland fine sand at the North Florida Research and Education Center – Suwannee Valley near Live Oak, FL.  The soil was prepared by rototilling to a depth of eight inches.  Beds were formed on 5-ft centers and were fertilized with 500 lbs/A of 13-1.7-10.8 (N-P-K) as they were formed.  Plots 100-ft long were arranged in a randomized split plot design with four replications.  Main plots were bed width and split plots were fumigation treatments. Bed top widths were 24, 28, 32, or 36 inches.  Fumigation treatments were metam potassium or untreated.  Metam potassium (K-Pam, AMVAC, Los Angeles, CA) was applied at 60 gallons per treated acre (based on area under the plastic mulch).

Soil was pressed to form beds six-inches high at the various widths using an adjustable width bed press (Kennco Mfg, Ruskin, FL).  Black high density polyethylene mulch (Sonoco, Charleston, SC) and drip tape (Robert’s RoDrip, San Marcos, CA) were applied to the preformed beds using a speed layer mulch applicator (Kennco Mfg).  Two drip tapes per bed were applied to each plot.  The drip tapes were positioned to be a distance one-third of the total bed width from each shoulder and three inches deep from the bed top.

Metam potassium was applied to treated beds on 13 March by using a mechanical proportioner (Dosatron, Clearwater, FL) set at an injection ratio of 1:50 (metam posassium:water, v:v).  Each injection of metam potassium for each bed width was conducted until the required amount was delivered for each bed width (Table 1).  The amount delivered to each plot was calculated based on the actual width of the bed as the treated area.  Untreated plots were watered for 240 minutes to fully wet the beds.

Purple nutsedge (Cyperus rotundus L) counts were taken on 31 March (18 DAT) and 12 April 2003 (30 DAT).  Counts were taken within each plot by dividing the treated bed into 3 sections, the two outside 6-inch sections (shoulder area) of the bed, and the remaining center area.  Counts were taken in this manner in a 5-ft long section of the bed.  Data were analyzed by analysis of variance and mean separation was done by Duncan’s Multiple Range Test.

Results and Discussion

Interaction.  There was no significant interaction between bed width and fumigation.  Therefore, the discussion will focus on bed width and fumigation treatments separately.

Bed Width.  Total bed and center bed nutsedge counts taken on 31 March were not significantly different among the various bed widths (Table 2).  Nutsedge counts from the shoulder area on 31 March showed the lowest number (228) in the 28-inch wide beds (Fig. 1) but were similar to counts in 24 and 32 inch wide beds.  The highest nutsedge population was found in the bed shoulder of 36 inch wide beds (Fig. 2), but was not significantly different from 24 and 32 inch wide beds.

Total bed nutsedge counts taken on 12 April were highest on 24 inch beds, but were not significantly different from 28 and 36 inch wide beds.  The lowest total bed nutsedge counts were found in 32 inch beds but were not significantly different in 28 or 36 inch beds.  The highest shoulder area nutsedge counts were found in 36, 24, and 28 inch beds.  No significant difference was found among bed widths for bed center nutsedge counts.  Overall, poor nutsedge control was found in all bed widths. 

Figure 1. Metam potassium treatment via two drip tapes on 24, 28, 32, and 36 inch wide beds. Figure 2. Metam potassium treatment via two drip
tapes on a 36-inch wide bed.

Fumigation Treatment.  Treating beds with metam potassium significantly reduced nutsedge counts on 31 March  in terms of total bed, bed shoulder area, and bed center area (Table 3).  Total bed nutsedge counts were reduced from 1254 to 471 per 100 linear bed feet with fumigation of metam potassium.  On 12 April, nutsedge counts were significantly reduced by metam potassium in total bed and bed shoulder area only.  However, on 12 April the bed center area only counts were not significantly different between the treated and untreated plots.  Metam potassium significantly reduced nutsedge counts compared to an untreated control, but the level of control provided was not acceptable.

Conclusion

In general, metam potassium applied via two drip tapes per bed reduced purple nutsedge populations by about 50% or more at 18 days after treatment.  However, by 30 days after treatment, the nutsedge populations in the bed center of treated vs. untreated beds were not significantly different.  Even treating the narrow bed width of 24 inches with metam potassium via two drip tapes did not adequately control purple nutsedge. 

Table 1.  Metam potassium delivery times for each bed width.

Bed Width
(in)

Injection Time
(min)

Rate per Treated Acrez (gal)

24

230

60

28

263

60

32

301

60

36

331

60

z Rate calculated based on the bed width of each treatment.

 

Table 2.  Effect of bed width on nutsedge populations for total bed, bed shoulder, and bed center on two dates.

Bed Width
(in)

Nutsedge (No./100 lbf)

31 March 2003

12 April 2003

Total

Shoulder

Center

Total

Shoulder

Center

24

926

424 abz

503

1128 a

569 a

608

28

613

288 b

325

898 ab

380 ab

440

32

824

411 ab

413

719 b

314 b

345

36

1089

586 a

503

1056 ab

571 a

488

 

NSy

 

NSy

 

 

NSy

z Means in a column followed by different letters not significantly different.
y Not significant.

 

Table 3.  Effect of metam potassium on nutsedge populations for total bed, bed shoulder, and bed center on two dates.

Fumigant

Nutsedge (No./100 lbf)

31 March 2003

12 April 2003

Total

Shoulder

Center

Total

Shoulder

Center

K-Pam

471 bz

220 b

251 b

789 b

226 b

505

Untreated

1254 a

634 a

620 a

1111 a

691 a

435

 

 

 

 

 

 

NSy

z Means in a column followed by different letters are significantly different.
y NS=Not significant.

(R. Hochmuth, E. Simonne, W. Davis, W. Laughlin, P. Vaculin - Vegetarian 03-10)


Miami-Dade Growers Conserve Water: the Challenges Ahead 

Water use, management, and quality along with gravelly loam soils (Fig. 1) are major issues in south Florida's Miami-Dade County where periods of flooding and drought are experienced occasionally.  Agricultural practices such as irrigation and fertilizer management potentially affect the water quality of the Biscayne Aquifer in the environmentally sensitive agricultural area adjacent to Everglades and Biscayne National Parks.  However, there is little documentation on the water conservation practices by the Miami-Dade County agricultural community and golf courses.


Fig. 1. The gravelly-loam (rock-plowed) soils pose a special water conservation challenges in Miami-Dade.

The University of Florida is conducting extension and research programs in Miami-Dade County to help the agricultural community conserve water, deal with flooding and drought, and improve irrigation and fertilizer management. A comprehensive survey of water conservation practices across commodity groups i.e., vegetables, tropical fruits, ornamental nurseries, and golf courses was conducted in 2000-2003 to help identify the practices these users adopted to conserve and protect their water supply.  The approach was to quantify the existing water management and irrigation practices and motivations for their adoption.  Over 600 agricultural and golf course water users in Miami-Dade County (a random sample) were asked to respond to a questionnaire about their current water-use practices.

The overall number of respondents was 30%.  Results generally showed an increase in water conservation practices during the last 20 years, although there still remain educational challenges to optimize water use while protecting the environment. Based on the responses, four areas of improvement have been defined:
 

  • Improvement of water delivery systems
    -          phase out of big-guns in vegetable crops by introducing economic alternatives (Fig. 2)
    -          introduction of low volume irrigation systems in golf
    -          increase adoption of low volume irrigation systems (ornamental operations).
  • Management practices
    -       
      record keeping for irrigation optimization (not regulatory!)
    -          periodic irrigation evaluation by Mobile Irrigation Lab
    -          integrating soil moisture monitoring with irrigation scheduling
    -          evaluation of alternative irrigation scheduling methods.
  • Water sources
    -          increase in the use of capped and cased wells where possible
    -          protection of wells and water sources
  • Integrate improved water management in BMP (Better Management Practices) development and adoption across all commodity groups in a “grass-roots” process (grower involvement).


Fig. 2. Irrigation guns (or “cannons”) are not an efficient
irrigation system for low water retention soils in the area but the economics of some crops make alternatives difficult.

The results and analysis of this water-use survey will be used in planning water-related extension and research programs for the community.

(Rafeal Muñoz-Carpena, TREC-Homestead - Vegetarian 03-10)

 
Choosing the Right Cover Crop for Rotation with Vegetable Crops

Summer cover crops have been shown to improve soil fertility, out compete weeds, enhance nutrient and moisture availability and help control many pests including nematodes in south Florida.  At the same time, they prevent nutrient and pesticide leaching and runoff and consequently improve subsequent crop yields and protect our environment. Growers investing in cover crops will certainly see benefits accumulate over the long term.

We are conducting field and pot trials at the Tropical Research and Education Center in Homestead to evaluate potential cover crops for south Florida vegetable growers.  Three leguminous summer cover crops, sunn hemp (Crotalaria juncea), velvet bean (Mucuna pruriens), and cowpea (Vigna unguiculata) are being compared with the already widely grown sorghum-sudangrass (Sorghum bicolor × S. bicolor var. ‘Sudanense’). The results show that sunn hemp, the fastest growing cover crops tested, can produce up to 12 Mt/ha of biomass, which is equivalent to more than 350 kg/ha of nitrogen, whereas sorghum-sudangrass produces only 5 Mt/ha with less than 50 kg/ha of nitrogen (Fig. 1).


Fig.1. Biomass produced expressed as the equivalent kg N per ha.

The summer cover crops can also reduce water and nutrient leaching by taking nutrients from soil, and accumulate them in their tissues. For example, in a pot study with a given irrigation rate, the NO3-N in leachate in the fallow treatment can be as high as 70 mg per pot, but with over crops, the NO3-N in leachate is less than 10 mg per pot (Fig. 2). 


Fig. 2. Amounts of NO3-N leached out of the root
zone with or without cover crops.

We found that the tomato yields and quality (e.g., extra large fruits) are increased when the tomatoes were grown in soil following a cover crop, especially following sunn hemp or cowpea (Table 1). Moreover, soil nematodes, especially the root-knot nematode, can be suppressed dramatically by growing and incorporating sunn hemp into the soil. Therefore, we recommend that growers grow either sunn hemp, or another legume as a cover crop on vegetable plots during the summer, and then incorporate the cover crop residues into the soil before growing vegetables during the fall and winter.

Table 1. Tomato marketable yields and quality following cover crops or fallow.

Cover crop

Marketable yield
(t ha-1)
Extra large fruits
(t ha-1)
Cowpea 18.0a 12.6a
Sunn hemp 18.1a 12.6a
Velvetbean 15.3b 10.6b
Sorghum sudangrass 16.2ab 10.8b
Fallow 15.3b 10.2b

(
Qingren Wang, Aaron Palmateer, Waldy Klassen, and Yuncong Li - Vegetarian 03-10)
 

Extension Vegetable Crops Specialists

Daniel J. Cantliffe
Professor and Chairman

Rafael Munoz-Carpena
Assistant Professor, hydrology

John Duval
Assistant Professor, strawberry

Mark A. Ritenour
Assistant Professor, postharvest

Chad Hutchinson
Assistant Professor, vegetable production

Steven A. Sargent
Professor, postharvest

Elizabeth M. Lamb
Assistant Professor, vegetable production

Eric Simonne
Assistant Professor and EDITOR, vegetable nutrition

Yuncong Li
Assistant Professor, soils
William M. Stall
Professor, weed science
Donald N. Maynard (retired)
Professor, varieties
James M. Stephens (retired)
Professor, vegetable gardening

Stephen M. Olson
Professor, small farms

Charles S. Vavrina
Professor, transplants
 

James M. White
Associate Professor, organic farming

Related Links
University of Florida
Institute of Food and Agricultural Sciences
Horticultural Sciences Department
Florida Cooperative Extension Service
North Florida Research and Education Center - Suwannee Valley

Gulf Coast Research and Education Center - Dover
UF/IFAS Postharvest

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