| VOLUME 5. NO. 12 | December 17, 1998 |
In This Issue: 1997 Melon Report Complete Rainfall Capture and Drip Irrigation Root and Vascular Diseases of Watermelon in South Texas |
1997 Melon Report Complete
The 1997 Annual Research Report to the South Texas Melon Committee has been completed and is available by request. This year's report includes work by ten different scientists from Texas A&M and U.S.D.A. Studies included in the report include: Gummy stem blight and black rot of melons; Susceptibility of cover crops to Monosporascus cannonballus; Control of Monosporascus root rot vine decline; Evaluation of DVC chitin technologies products on yield of cantaloupe; Variety evaluations; Development of melon breeding lines and cultivars adapted to the LRGV; Evaluation of melon plant introductions for resistance to Monosporascus cannonballus; Evaluation of MRRVD field tolerant lines and hybrids in the field and greenhouse; Spring 1997 Permit herbicide trial on direct seeded honeydew melons.
If you would like to receive a copy of the 1997 melon report you can request one by calling (956) 968-5585, written requests can be sent to Marvin Miller at the Texas A&M Research & Extension Center, 2415 East Hwy. 83, Weslaco, TX 78596.
Rainfall Capture and Drip Irrigation by Frank Dainello
Although drought conditions are somewhat alleviated around the state, vegetable producers in South Texas are still in a bind for water. In the future as the state's population continues to grow and less water is available for crop production, we will see an increased need for the use of water conservation methods. This coupled with the not so unusual circumstances of drought in the state will cause agriculture to adapt and use as many advanced water conservation technologies as are available.
In an attempt to encourage the adaption of the most advanced techniques for managing limited water resources in vegetable production, a team of scientists from the Texas Agricultural Extension Service conducted a series of demonstrations in the Winter Garden area. The results of these two demonstrations are presented in this article.
The initial demonstration conducted by the Vegetable Crops Water-Use Efficiency Team was established in cooperation with McFaddin Farms of Uvalde, Texas. In this demonstration, water-use efficiency of a Rainfall Capture system (RFC), and drip irrigation plus plastic mulch, was compared with that of conventional furrow irrigation in cantaloupe production. Drip irrigation was scheduled, based on soil moisture tension as indicated by tensiometer at a 12 inch depth. When 45 centibars tension was reached, one inch of irrigation water was applied. The cooperator scheduled the irrigation in the furrow block using his normal procedure. No supplemental water was applied in the RFC block.
The RFC system was established on October 26, 1993 in order to capture and store sufficient moisture throughout the fall and winter months for use on cantaloupe to be grown the following spring. This system consisted of establishing two polyethylene lined mini catchment basins, 22 inches apart on an eighty inch wide raised bed. Each basin was approximately 10 inches wide across the top, 4 inches deep, and 3 inches wide across the bottom. Holes spaced 3 feet apart were punched in the bottom of the lined catchment basin to allow moisture to enter the bed for storage. The drip and furrow irrigated blocks were established on April 4, 1996 and all blocks were direct seeded with the cantaloupe variety 'Caravelle' on April 12. Fruit yield and water use data obtained in this demonstration are presented in Table 1.
A second demonstration was established in 1995 in conjunction with Cargil Farms of Uvalde. In this demonstration, comparisons were made between drip irrigation, RFC and plastic mulched furrow irrigated blocks. Due to weather conditions and scheduling conflicts, the RFC system was established just prior to planting on April 6. All blocks were direct seeded, using 'Mission' by April 15. The data obtained from this demonstration is shown in Table 2.
Drip irrigation greatly increased yields compared to furrow irrigation, at both locations (25,812 lbs/acre and 29,621 lbs/acre, compared to13,367 lbs/acre and 16,988 lbs/acre), respectively, for the drip and furrow irrigated blocks. In addition, applied water was reduced 16-20 inches in the drip blocks, respectively, at the Cargil and McFaddin locations. Surprisingly, under the conditions of these demonstrations, the RFC system resulted in higher yields than furrow irrigation.
A good measure of applied water use efficiency is the ratio of total gallons of water applied to pounds of fruit produced. Ratios of 4.3 to 1 and 50 to 1 were obtained at the McFaddin site from drip and furrow, respectively, whereas 7.4 to 1 and 33.4 to 1 were reported at the Cargil location.
Approximately the same total volume of water (rainfall + irrigation water) was required to produce a cantaloupe crop exceeding 25,000 lbs/acre with drip irrigation in both years of these demonstrations: 17 inches. In 1994, 4 inches of irrigation water was applied, via drip, while 13 inches was received from rainfall. In 1995, 8 inches of drip irrigation water was accompanied by 9 inches of rainfall. Although sufficient rainfall was received during these demonstrations to enable a crop to be produced, fruit size was slightly reduced. Consequently, RFC alone is not a viable replacement for irrigation, but rather a supplement to irrigation in most areas. Additional work is needed to determine what effect RFC can have on the needs of crops watered by drip, furrow, and sprinkler methods.
Although both systems can increase production costs significantly, they may be required for successful production in the future if drought conditions persist and/or water for production becomes limited as a result of increasing population.
For more information regarding these demonstrations contact: Dr. Frank Dainello, Extension Vegetable Specialist, Department of Horticulture, Texas A&M University, College Station, TX, (409) 845-5341; Dr. Larry Stein, Extension Horticulturist, Texas A&M Research & Extension Center Uvalde, TX, (830) 278-9151; Mr. Kenneth White, County Extension Agent-Agriculture, Uvalde, TX, (830) 278-6661; Dr. Guy Fipps, Extension Agricultural Engineer-Irrigation, Department of Agricultural Engineering, Texas A&M University, College Station, TX, (409) 845-7454.
Table 1. Cantaloupe Yield in Response to Supplemental Water Application Techniques, McFaddin Farm, 1994.
| Supplemental water application technique | Marketable yield (lbs/A) | % Cull yield | No irrigations - water applied (in/A - gpa) | Ratio gal. water applied to lb. fruit produced |
| Drip irrigation +plastic mulch | 25,812 | 3 | 4 (4.04") 109702 | 4.3 : 1 |
| Rainfall capture * | 20,990 | 9 | 0 (0) 0 | 0 : 1 |
| Conventional furrow irrigation | 13,367 | 33 | 3 (24.6") 667899 | 50 : 1 |
* Rainfall received: Oct. 26, 1993 (RFC establishment) to April 12, 1994 (planting) = 14.04"
April 12, 1994 (planting) to July 26, 1994 (end of harvest) = 13.12"
Table 2. Cantaloupe Yield in Response to Supplemental Water Application Techniques, Cargil Farm, 1995.
| Supplemental water application technique | Marketable yield (lbs/A) | No irrigations - water applied (in/A - gpa) | Ratio gal. water applied to lb. fruit produced |
| Drip irrigation +plastic mulch | 29,621 | 8 (8.10") 481984 | 7.4 : 1 |
| Rainfall capture * | 20,038 | 0 (0) 0 | 0 : 1 |
| Conventional furrow irrigation | 16,988 | 3 (24.6") 834986 | 33.4 : 1 |
Rainfall received: April 12, 1995 (planting) to July 13, 1995 (end of harvest) = 9.65"
Root and Vascular Diseases of Watermelon in South Texas by Tom Isakeit
Diseases that affect the roots and vascular system of watermelon plants cause wilting of vines and leaves. Thus, when attempting to diagnose the cause of wilting, it is essential to examine the roots and crowns of affected plants. The pathogens involved in these diseases are soilborne and, with the exception of nematodes, are very difficult to manage. However, the effects of these pathogens when they infect roots or stems are generally not as devastating as diseases caused by foliar pathogens, except in soils where the watermelon crop has been grown frequently and the pathogen has built up to high levels. One of the reasons for this is that soilborne pathogens are not mobile like foliar pathogens and so will not spread as rapidly throughout the field. (Soilborne pathogens can be very devastating when they infect fruit; this will be the subject of another article).
Damping-off is a disease that affects young seedlings. Seedlings wilt and die, or seeds may not emerge. Damping-off is caused by fungi: Rhizoctonia solani or several species of Pythium. Generally, damping-off operates best at low temperatures that are sub-optimal for germination and growth of watermelon. However, I have documented the presence Pythium aphanidermatum in several areas of south Texas. This particular species grows optimally at high temperatures and I have seen it killing newly-transplanted watermelons during a period of warm weather. Watermelon seeds are usually treated with broad-spectrum contact fungicides that would protect against all damping-off pathogens, but these are of limited value once the seed germinates and starts growing. Nothing can be done if seedlings are growing under conditions favorable for R. solani, but soil applications of Ridomil Gold will provide protection against Pythium species.
Nematodes can substantially reduce yield of watermelon. The affected plants are stunted and chlorotic. Root-knot nematodes can cause galling on roots, but there are no visible root symptoms with the reniform nematode. However, I have never seen any evidence of nematode problems in watermelon production in south Texas and for this reason, I recommend testing soils for the presence of nematodes rather than routinely treating with nematicides. There is good information about the distribution of these nematodes in the Lower Rio Grande Valley, based on surveys conducted over a 22-year period. The root-knot nematode occurs primarily in sandy soils and it has been well-documented in the Rio Grande City area, as well as northern portions of Hidalgo county. Sandy soils in the Premont and Falfurrias areas could support the root-knot nematode, but I have not seen any problems in these areas. The reniform nematode occurs in fine textured soils (high amounts of silt and clay), predominantly in areas of the Valley where watermelons are not grown, although this nematode has also been documented in the northern portion of Hidalgo county. Although nematicides can provide an economical control, a crop rotation with corn or sorghum and a weed-free fallow can reduce numbers of nematodes below damaging thresholds.
Fusarium wilt is a soilborne disease caused by the fungus Fusarium oxysporum f. sp. niveum. The first symptom is a temporary wilt of vines, which occurs during the hottest part of the day. The wilt becomes permanent and progressive, affecting more vines. Eventually, the plant dies. If a cross-cut is made in the stem, a brown discoloration of the vascular system can be seen. The best place to see this discoloration is near the crown, especially if the vines are only slightly wilted. The roots are not affected. The disease is controlled by the use of resistant cultivars, however, there are no commercially-available varieties that are resistant to Race 2 of this pathogen, which I have documented in some of the sandy soils of northern Hidalgo county and the Falfurrias-Premont area. This pathogen will persist for years in soil in the absence of watermelon. Rotations of 5-7 years are recommended, but even longer periods of time may be required to reduce pathogen populations. I have not seen this disease occurring in heavy, alkaline soils of south Texas.
Anasa wilt, caused by a toxin produced by the squash bug, can be mistaken for Fusarium wilt. This problem is associated with watermelon growing next to brush and squash bugs can be seen on some of the plants.
Monosporascus vine decline is caused by another soilborne fungus, Monosporascus cannonballus. It seems to operate in the soils that Fusarium wilt does not occur in, namely, the heavy, alkaline soils in the Lower Rio Grande Valley. It is most prevalent in the Rio Grande City area, where fields have been cropped extensively with cantaloupe. It is less common in other areas of the Valley. It causes a sudden, permanent wilt of vines. Sometimes there is vascular discoloration, but this is not a reliable diagnostic feature. Discrete, dark brown lesions can be found on the roots. There are no control measures for this fungus.
Other pathogens may be involved in wilting, but their pathogenicity has not been demonstrated and until further information is gathered, no recommendations can be made. For example, Rhizoctonia solani and a Pythium sp. were isolated from roots which had a light brown discoloration.
Southern blight is caused by the fungus, Sclerotium rolfsii, which thrives under moist soil conditions at high temperatures. I have seen this on one occasion, in mid-Hidalgo county, affecting watermelon growing under drip irrigation and plastic mulch. The symptoms are wilting and a white, prolific cottony growth of the fungus in the crown area. The fungus later produces brown, spherical resting bodies, which resemble mustard seeds. This is not an important disease of vines, but under certain conditions, it can cause a fruit rot (which could be minimized through the use of drip irrigation and plastic mulch).
Lynn Brandenberger/Editor
The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.