R. J. Thullen and P. E. Keeley

OBJECTIVES: To identify effective systems for the control of annual morningglory in cotton.

PROCEDURES: Several treatments were applied to field plots at the USDA Cotton Research Station in 1989 and 1990 for the control of annual morningglory in cotton. Herbicides were first applied to planting beds at cotton planting in early April and incorporated with a mulcher operated 5 em or 10 em deep in the soil. Rates for these early treatments were 2. 0, 2. 0, and 1. 6 lbs/A, respectively, for cyanazine, methazole, and prometryn. Post emergence and layby treatments were applied as directed sprays to weeds in the drill row at the base of the cotton plants. Post-emergence treatments began soon after the middle of May, whereas the layby treatments were not applied until the end of June. Rates were 1.0 lb/A for cyanazine, 0.5 to 1.5 lbs/A for methazole, and 0.7 to 1.6 lbs/A for prometryn. Although all plots were conventionally cultivated, some were cultivated with special equipment (rods/torsion weeders/spring weeders) to remove small morningglory in the drill row of cotton. When rods were used, plots were cultivated in opposite directions. This cultivation and handweeding were both performed near the end of May. See Table 1 for more information about treatments.

RESULTS: The most successful herbicidal treatment for the control of annual morningglory in cotton was postemergence applications of 1.0 lb/A cyanazine + 2.0 lbs/A MSMA in early June (Table 1). Applications of cyanazine + MSMA to cotton at layby in late June was also helpful in reducing yield losses of cotton. The only other herbicide that provided significant postemergence activity was prometryn. Prometryn incorporated 10 em deep provided the most consistent control of the soil-incorporated herbicides. But control with this treatment was incomplete based on both visual control ratings and harvested cotton (Table 1). Although the cultivator equipped with rods removed many small morningglory plants in the drill row of cotton, too many survived. Based on the results of the handweeding treatment in late May of 1989 and 1990, the weed-free period for morningglory will probably have to extend at least until the middle of June.

FUTURE PLANS: A manuscript of this two year study is being prepared. A second study will begin on the area of this morningglory nursery in the spring of 1991.

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P. E. Keeley and R. J. Thullen

OBJECTIVES: To determine why control of nightshade with prometryn declined with time in a field study conducted in 1985, 1987, 1988, and 1989.

PROCEDURES: Both seed and soil samples were collected from field plots previously untreated and treated with prometryn. Treated plots were those where rates of prometryn from 1.5 to 2.0 lbs ai/A originally controlled black nightshade in 1985 and 1987 but failed to control nightshade in 1988 and 1989. Untreated plots were the weedy-check plots of the 1985 to 1989 study that had never been treated with a herbicide. Soil samples from the field in early 1990 were treated with 2.00 ppm prometryn and bioassayed in the greenhouse with black nightshade at weekly intervals for 7 weeks. Seed from field plots, which had been collected earlier, was planted into soil freshly treated with 0.25, 0.50, 1.00, and 2.00 ppm prometryn.

In addition to the experiments described above, a final field study was initiated on April 18, 1990 to determine if nightshade had developed some resistance to prometryn or if previously treated soil was now degrading prometryn at some accelerated rate. Plots, 19 m long by 4 m wide, which were treated during 1985 to 1989, were treated in a perpendicular direction with a 4 m band of 2.0 lbs/A of prometryn. The soil was left flat after treating and the
herbicide was incorporated into the soil with a mulcher operated at 10 em deep. The area was sprinkle irrigated at 3 to 5 day intervals for the following 36 days. Total sprinkling time was 35 hours, and total amount of water applied was 9 em. Black nightshade seedlings were counted in treated and untreated strips of all plots 4 weeks after treatment, and visual weed control ratings were recorded at 4 and 6 weeks after treatment.

RESULTS: Degradation of prometryn in the greenhouse appeared to occur at approximately equal rates in soil collected from field plots previously treated or untreated with prometryn. Residues from applications of 2 ppm of prometryn killed all nightshade seedlings for 3 weeks. When some plants began surviving at 5 and 7 weeks after treatment, dry matter production of nightshade was similar in soils previously treated and untreated with prometryn. Nightshade seedlings from seed collected from plots treated with prometryn responded similarly to increasing rates of prometryn under greenhouse conditions as seed collected from untreated plots. Herbicidal activity was sufficiently great from applications of as little as 0.25 to 0.50 ppm to kill most seedlings, and very little growth occurred at 1.0 ppm of prometryn.

When prometryn was applied in perpendicular strips 4 m wide across plots previously untreated and treated with prometryn, no black nightshade seedlings survived for 4 weeks (Table 2). Even at 6 weeks after treatment, visual control ratings of weed seedlings were still 99 to 100%. The fact that control in 1990 was complete for 6 weeks indicates that nightshades have not developed appreciable amounts of resistance to prometryn and degradation of prometryn probably occurred at normal rates. Furthermore, the excellent control obtained indicates that the herbicide was not readily leached from the upper 2.5 em of soil where the majority of the weed seeds germinate. Since efforts failed to provide evidence for the movement of the herbicide with water, the development of weed resistance to prometryn, or accelerated degradation of this herbicide in soil, increasing weed populations were suspected of contributing greatly to the declining nightshade control from prometryn. It is suspected that, if numbers of seedlings estimated ha-1 in Table 2 represents only 10% or less of the soil seed reservoir, weed seed populations have increased from 85 million in 1985 to as much as 800 million in 1990.

FUTURE PLANS: A manuscript reporting the results of this study has been written and was submitted for consideration for publication in Weed Technology Journal.

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W.C. Hofmann, L.M. Carter, P.E. Keeley, and L.F. Elliott J.H. Chesson, R.J. Thullen, D. Ballard, and N. Goodell

OBJECTIVES: To develop the criteria for ‘best practice’ cotton production systems. To test experimental component subsystems and the interrelationship of cotton production subsystems including rotational crops. To demonstrate for technology transfer ‘best practice’ systems.

PROCEDURE: Four systems were identified for inclusion in a
field study resulting from a factorial of two systems categories: row spacing and tillage. The ‘best practice’ row spacing was selected as 30 inch as compared to the common practice of 38/40 inch spacing. As the ‘best practice’ tillage, the zone system with precision tillage and controlled traffic was selected to be compared to the common broadcast tillage system. The factorial arrangement allowed: 1} a ‘farmer practice’ 38/40 inch system; 2} a ‘farmer practice’ adaption using 30 inch row spacing; 3} a zone system treatment using 38/40 row spacing; and 4} the best practice system using both zone concepts and 30 inch row
spacings. Treatment 1 and 3 were managed with 6 38-inch row equipment and were 12 rows wide. Treatment 2 was managed with 8 row 30 inch equipment and was 16 rows wide. Special equipment was developed for the best practice treatment #4 using 9-row 30- inch row equipment with wide furrows every three rows for
traffic. In 1989 the south portion of the study was planted using a factorial layout with 6 replications of plots arranged in such a way that cross tillage could be applied to the two farmer practice treatments. The plot size varied by treatment in width with all treatments approximately 300 feet long. In 1990 the north portion was planted using the same arrangement with a different randomization to allow a rotation variable with alternate years. Sampling consisted of soil and petiole fertility, soil and plant water stress and yield.

RESULTS: Measurement of petiole samples shows that the best practice treatments were nitrogen deficit at the end of the growing season compared with the farmer treatments. We surmise that the best practice treatments with the increased water infiltration allowed greater percolation of water and thus greater loss of nitrogen by leaching. Attempts at differential irrigation based upon soil or plant water stress were frustrated by the approximate 7 to 10 day irrigation demand confounded with the need for dry periods for cultivation and water scheduling. Due to obvious and extreme variability in plant growth within plots a covariant was sought. There appeared to be a correlation between sandy areas in the plots and plant height therefore each plot was mapped and the percentage sand soil calculated. With a covariance analysis the estimate of the sand effect was -3.45 (lbs/a) / (% sand) for the 1989 yield data and -3.25 for 1990 in the south test. No correlation was evident for the north test.

Using contrasts among the least square means for the south test and contrasts among the GLM means for the north test, the yield data show important differences among treatments. The first year data for both the south and north tests show that the 38 inch systems yields were 4 to 7 percent greater than the 30 inch systems. Also for the first year both tests indicated no difference in yield between zone and broadcast systems. During the second year (which can be determined only for the south test) the trends reversed: 1) there was no detectable difference between row spacings and 2) the zone system yielded 8.6% more than the broadcast. The change from no difference to a difference between zone and broadcast can be explained by noting that the treatment effect did not exist at the initiation of the plots but was developed during the first year. The 30 inch vs 38 inch differences is difficult to explain since most studies on the station have shown substantial increases with 30 inch

FUTURE PLANS: The study became a nightmare in management. The size of the field test, the time to convert equipment, constraints on irrigation timing and lack of personnel and funds for collecting and processing samples compromised the study and no reasonable solution within the resources available could be found. Therefore the study was abandoned with plans to develop a small scale study to evaluate in depth certain of the questions identified by the large study.

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L. M. Carter and J. H. Chesson

OBJECTIVES: To adapt, modify or design planters and planter controls for direct seeding into cover crops.

PROCEDURE: Determine desirable and achievable planting conditions associated with direct seeding into cover crops, including type of cover crop, method of vegetation suppression and preparation prior to planting. Test operation and performance of unmodified cross slot planter designs. Design mechanisms and procedures for improving performance to acceptable levels. Investigate application of other planter designs and procedures for direct seeding into cover crops.
PROGRESS: Combining two years experience with the unmodified cross slot planter design, six conclusions can be stated: 1) the design is acceptable only within a narrow range of application which includes the original design criteria, ie dry soil planting of grains; 2) the depth of planting varies greatly with soil tilth and moisture with all seeds; 3) the design without modification is unsuited for cotton either for planting into cover crops or into prepared soil; 4) cotton planted into cover crops with this design requires rain or simulated rain for emergence; 5) cotton planted into prepared moist soil did not emerge or the emergence was well below any acceptable standard;
6) cotton planted into dry prepared soil with postplant irrigation emerged acceptably.

     The heavy footprint of the gage-wheel-furrow-closure component was determined to be the cause of poor performance as described in conclusions 2, 3, 4, and 5. A mechanical-hydraulic servo control was designed as a combination seed depth control and footprint pressure control. The design was tested and found to perform as anticipated allowing control of seed depth within .25 inch and accurate control of footprint pressure. With the control operating seed emergence in prepared moist soil was comparable to ‘normal’ planters. With cover crops, the closure pressing could be increased and controlled for improved, if not completely adequate, emergence. The mechanism for the control was described for possible patent and therefore has not been disclosed to the public. Application to other existing designs was claimed in the patent description.

The operating parameters of the control will be documented and will be determined. Depending upon interest, the control may be developed for technology transfer beyond publication of any potential patent.

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L. M. Carter and J. H. Chesson

OBJECTIVES: To develop apparatus and instrumentation for field scale survey-measuring salinity based upon theories developed by the USDA Salinity Laboratory, Riverside, CA.

PROCEDURE: The probe design was based upon earlier reported research by Carter. In concept the probe compacts a ribbon of soil .75 inch wide at the depth of operation using a curved wedge. The soil strain of .5 inch has been determined in the past for maximum mechanical compaction. To remove the surface organic material from the contact area, a forward sweeping tine was attached to the front of the probe. A five probe design, rather than the classical 4-probe design, was chosen to allow symmetrical operation behind a tractor in bedded soils. This configuration allows a probe in each of 5 furrows with the inter- probe distance fixed at the row spacing. For non-bedded soils the inter-probe distance can be varied between 20 and 42 inches. A folding 3-point mounting tool bar was designed with a detachable highway compatible truck for transportation behind a pickup. The system was designed so that one or two people could attach the tool to a tractor and prepare the system for operation within 5 minutes.

RESULTS: The system was tested in dry and wet soils without instrumentation for integrity as a tillage tool. Operation was found feasible beyond 6 mph. The instrumentation package was attached including the 5 probe monitor and geographic position sensor. The instrumentation was calibrated by Dr. Rhoades in a
very saline soil.

FUTURE PLANS: The system will be field calibrated for variability with respect to speed, moisture, and soil types and field tested for suitability to task as the Shafter contribution to the cooperative program. At completion the system will be used to map salinity of several large agricultural areas. The future plans include development of a method and apparatus to utilize a electromagnetic sensor as a measure for salinity.

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L. M. Carter, W. c. Hofmann, and J. H. Chesson

OBJECTIVES: 1. To determine the efficacy of deep application of a fumigating nematocide. 2. To develop safe and environmental acceptable methods of applying nematocides.

PROCEDURE: The 1990 study consisted of 6 treatments: a control plot with normal tillage and no nematicide (treatment A); a normal 8 gallon per acre (gpa) Telone application with 2 shanks 10 inches to each side of the intended drill operated 10 inches deep (treatment B); a 22 inch deep precision tillage control plot with no nematicide (treatment C); and 22 inch deep precision tillage application at rates of 4, 6, and 8 gpa of Telone (treatments D, E, and F). The precision tillage tool consisted of two 32-inch long sub-soil shanks mounted to a tool bar with disk type bedders mounted behind the bar on pivoting arms which allowed constant depth of furrowing. The subsoil shanks had a forward angle of 15 degrees and were operated 22 inches deep from original soil level (depth from the top of the resulting bed was approximately 32 to 34 inches) . For nematocide application, a .25 inch ID tube was welded to the trailing edge of the subsoil shanks to release the nematocide at the bottom of the slot. All nematocide treatments were applied with an experimental metering device which was controlled by ground speed and depth. A peristaltic metering pump was used for each applicator. The speed of the meter was controlled by a electro/hydraulic servo commanded by a rotary pulse sensor attached to the ground metering wheel. The metering wheel was mounted such that the meter would only operate when the shanks were deeper than 50% of the intended depth. The field chosen was known to have a high and fairly uniform population of nematodes. The treatments were applied in a latin square design (6 replications) to allow greater control over nematode population variability. Two weeks after treatment application but before planting cotton, soil samples from the 1st, 2nd, and 3rd foot were obtained from each plot and placed in small pots with a seedling tomato plant. An estimate of the initial nematode population for each plot was obtained by rating the degree of nematode galling in the tomato roots on a scale of 0 to 4 with 0 indicating no galling and 4 indicating severe galling.

RESULTS: Predictably, the application of 8 gpa of Telone with a normal application reduced the galling on tomatoes to a low level. However, that same reduction was obtained with 6 gpa applied with precision tillage. Even at the 4 gpa rate applied with precision tillage the nematode galling was drastically -2- reduced suggesting that the efficiency of Telone can be substantially improved with deep application. Both applications methods were most effective in reducing the population in the second foot. We believe it is important to note that the effectiveness was greater for precision tillage application in the third foot compared to normal application. There was an improvement in cotton yield related to precision tillage and to rate of Telone. With no nematicide, precision tillage increased the yield by 10%. However at 8 gpa of Telone the increase for precision tillage (tillage effect only) was 34%. The increase in yield with 8 gpa using normal application equipment was 16%. One way of interpreting these data is that precision tillage reduced the soil compaction limitation to root extension and the Telone reduced the nematode population, each contributing the increased yields. However, when the tillage effect and the nematocide are combined, the yield increase is greater than the sum of the individual effects. Perhaps a more important interpretation is that the low rate of 4 gpa of Telone applied with precision tillage produced a 19% yield increase compared to 8 gpa applied with normal equipment. These data suggest the possibility of dramatically reducing the applied rate of Telone with equal or better yields. An application of these findings could result in a two-fold advantage for the farmer, 1) lower input cost with greater yield and 2) reduced chemical applied to the soil and therefore less release to the air. The metering system was judged to be practical for use by farmers. For farmer use, 1) higher quality (ie longer life) peristaltic meters should be purchased, 2) commercial sized, approved tanks, tubing and valves would be needed, and 3) the supply tubes to each shank should be equipped with a positive pressure-operated check valve. The experimental system prevented leakage during turns and reduced variation in application rate resulting from wheel slippage and acceleration or deceleration at ends of fields. With the deep application, there was absolutely no noticeable odor of the Telone suggesting that the method may meet the most stringent environmental rules.

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