PLANT PATHOLOGY SERIES TIMELY INFORMATION Agriculture & Natural Resources

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1 PLNT PTHOLOGY SERIES TIMELY INFORMTION griculture & Natural Resources EXTENSION PLNT PTHOLOGY, S. DONHUE DRIVE, UURN UNIVERSITY, L - July, PP- Impact of Cropping Sequence on Diseases, Nematodes, and Yield of, Cotton, and in Southwest labama. K. Hagan, K. L. owen, H. L. Campbell, and K. L. Lawrence Department of Entomology and Plant Pathology, uburn University, L M. Pegues and J. Jones Gulf Coast Research and Extension Center, Fairhope, L INTRODUCTION s (rachis hypogaea), cotton (Gossypium hirsutum), and corn (Zea mays) are important agronomic crops in labama. In, labama s cotton, corn, and peanut production were ranked th, th, and rd respectively, among states nationwide. Rotation is among the most effective tools for maximizing the crop yields while minimizing the impact of diseases and plant parasitic nematodes on crop quality and yield. study was begun in at the Gulf Coast Research and Extension Center in Fairhope L to assess the impact of crop rotation on disease and nematode pests of peanut, cotton, and corn. The study site was previously planted to corn, peanut, and other assorted crops but not to cotton. Nematode pests of peanut, cotton, and corn have not been previously indentified on this site. Late leaf spot (Cercosporidium personatum), rust (Puccinia arachidis), and to a lesser extent stem rot (Sclerotium rolfsii) had previously been reported on the study site in peanut. PRODUCTION METHODS The study area was turned with a moldboard plow and then bedded in February or March. The experimental design was a randomized complete block with four replications. Plots for individual rotation sequences consisted of eight rows on inch centers that were feet in length. nnual soil samples were taken to monitor soil fertility. Fertilization and weed control practices were according labama Cooperative Extension System recommendations. The study was not irrigated. While DKC - corn was planted in mid-late March, DPL or DPL cotton and either Georgia-L or Georgia Green peanut were sown at recommended rates in May. Temik G at. lb/ was applied in-furrow to cotton and peanut for thrips control. was combined in ugust. The plant growth regulator Pix was applied as needed to cotton. Cotton was prepared for harvest with Diuron + Dropp W + Prep. Cotton plots were picked in September or October. Full canopy sprays of ravo Weather Stik F were made for leaf spot and rust control. s were harvested in October. Pod yields are reported at % moisture. DISESE ND NEMTODE SSESSMENT The occurrence of foliar diseases in corn was visually assessed on the ear leaf on a to scale where = no disease, = to %, = to %, = to %, = to %, etc of leaf area LM &M ND UURN UNIVERSITIES, ND TUSKEGEE UNIVERSITY, COUNTY GOVERNING ODIES ND USD COOPERTING The labama Cooperative Extension System offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.

2 diseased. Early and late leaf spot were rated using the - Florida peanut leaf spot scoring system where = no disease, = very few lesions in canopy, = few lesions noticed in lower and upper canopy, = some lesions seen and < % defoliation, = lesions noticeable and < % defoliation, = lesions numerous and < % defoliation, = lesions very numerous and < % defoliation, = numerous lesions on few remaining leaves and <% defoliation, = very few remaining leaves covered with lesions and < % defoliation, and = plants defoliated or dead. Rust was assessed using the ICRIST - rating scale where = no disease and = to % of leaves withered. In peanuts, stem rot hit and TSWV counts ( hit was defined as < ft of consecutive stem rotdamaged plants per row) were made after plot inversion. Soil samples for a nematode assay were collected at or shortly after harvest, and processed using the sugar flotation method. RESULTS Cotton - During the year study period, no foliar diseases were noted in cotton. High numbers of root knot nematode juveniles were occasionally recovered from from plots cropped to cotton, particularly in (Table ). Root knot juvenile numbers were not impacted by cotton cropping frequency. Subsequent analysis showed that the southern root knot nematode (Meloidogyne incognita Race ), which is not a parasite on cotton, was present. Concurrent to the recovery of high numbers of root knot juveniles from selected plots, root galling was noted on smallflower morningglory (Jacquemontia tamnifolia). Highest juvenile counts were recorded from those cotton plots infested with the above weed. Table : Impact of cotton cropping frequency on root juvenile counts and lint yield. Cotton cropping frequency Root knot juvenile counts Z Every year (+ years) -- Y a a a a a Every nd year a a a a a a Every rd year a a -- a a -- Every th year a Consecutive years a -- a a a a Consecutive years a a -- Lint Yield (lb/) Every year (+ years) -- Y a a a a a Every nd year a a a a a a Every rd year a a -- a a -- Every th year a Consecutive years a -- a a a a Consecutive years a a -- Z Number of southern root knot nematode juveniles (M. incognita Race ) per cc of soil recovered. Y -- = Rotation pattern not evaluated in study year. X Means in each column that are followed by the same letter are not significantly different (P<.).

3 In the absence of damaging populations of the cotton root knot or reniform nematodes, cotton cropping frequency had little impact on lint yields (Table ). Continuous cotton yields did not greatly differ for cotton cropped behind one, two, or three years of either the corn or peanut rotation partners. Figure : Impact of previous crop on the lint yield cotton, -. Yield (lb lint/) Yield (lb lint/) Yield (lb lint/) Yield (lb lint/) Yield (lb lint/) Yield (lb lint/) Cotton Cotton From through, previous crop impacted cotton yield in only when lint yield was lower for cotton following cotton as compared with corn, while yield response for cotton following peanut was intermediate (Figure ). Elevated root knot juvenile populations were noted in cotton in and (data not shown). In both years, juvenile counts were lower in cotton following peanut as compared with the cotton behind cotton or corn. - In some years, cropping frequency had a significant impact on leaf spot intensity, pod yield and to a lesser extent TSWV and stem rot incidence in peanut. With the exception of and to a lesser extent in and, TSWV (tomato spotted wilt virus) pressure was low during the study period (Figure ). cropping sequence impacted TSWV levels in and (data not shown). In both years, was often lower when peanut followed a minimum of one year of cotton or corn as compared with peanut. In addition, previous crop significantly impacted in peanut. In,, and, incidence of TSWV was higher in peanut following peanut as compared with cotton. cropped behind corn also suffered less TSWV damage than peanut following peanut in and.

4 Figure : in peanut as influenced by previous crop, -. Late leaf spot was the dominant leaf spot disease present. Over year study period, leaf spot intensity was higher in,,, and for continuous peanut when compared with peanut cropped after one year of either cotton or corn (Table ). Further reductions in leaf spot intensity were noted in and, when two or three years of cotton and/or corn, respectively, proceeded peanut. When peanut was cropped for two consecutive years in and, leaf spot intensity levels were similar to ratings for continuous peanut. With the exception of and, leaf spot intensity was significantly influenced by previous crop (Figure ). When compared with peanut as the previous crop, significant reductions in leaf spot intensity were noted in four and five study years in peanut cropped behind corn and cotton, respectively. With the exception of when leaf spot intensity was lower in peanut following cotton as compared with corn, similarly low disease ratings were recorded in peanut cropped behind cotton and corn.

5 Table : Cropping frequency impacts leaf spot intensity and stem rot incidence in peanut. cropping frequency Z Every year (+ years). a Y. a. a. a. a. a. a Every nd year. b. ab. a. a. b. b. b Every rd year -- X. b. a --. b. c -- Every th year a c Consecutive years a a W Every year (+ years). a. a. a. a. a. a. a Every nd year. a. a. a. a. a. a. b Every rd year --. a. a --. a. a -- Every th year a b Consecutive years a a Z Late leaf spot was rated using the Florida to leaf spot rating scale just prior to plot inversion. Y Means in each column that are followed by the same letter are not significantly different (P<.). X -- = Rotation pattern not included in study year. W is expressed as the number of hits per row feet. Figure : in peanut as impacted by the previous crop. ase C

6 In contrast to leaf spot diseases, cropping frequency had limited impact on stem rot incidence in peanut (Table ). In some years such as and, stem rot incidence in peanut was so low that counts for the continuous, one year out, and two year out peanut rotations were similar. Surprisingly, peanut cropping frequency also had little impact on stem rot incidence under moderate to high pressure in through. In, higher stem rot incidence was noted two or more consecutive years of peanut as compared with peanut after one or two years of either cotton or corn. s was the case with cropping frequency, previous crop also had limited impact on stem rot intensity in peanut (Figure ). cropped behind cotton and corn suffered less stem rot damage as compared with peanut following peanut only in and. In all other study years, similar stem rot indices were recorded in peanut regardless of the previous crop. Figure. Previous crop has limited impact on stem rot incidence in peanut. With a few exceptions in plots heavily colonized by morningglory, root knot juvenile counts in plots cropped to peanut were very low and were not impacted by cropping frequency or previous crop in any study years (data not shown). In three of seven study years, pod yield was influenced by peanut cropping frequency (Table ). The value of crop rotation as a tool for enhancing peanut yields was first noted in the nd study year, when higher pod yields were obtained for peanuts cropped behind one year of either cotton or corn as compared with two successive years of peanut. While similar yields were noted regardless of peanut cropping frequency from through, sizable numerical differences in pod yield were noted, particularly in and when peanut followed peanut. In contrast, sizable yield gains were not always noted where peanut followed two or three as compared with only one year of cotton or corn.

7 Table : Impact of cropping frequency on peanut pod yield. cropping frequency Yield (lb/) Every year (+ years) -- Z -- a a a c c Every nd year a Y a a a a a b Every rd year -- a a -- a b -- Every th year a a Consecutive years b a c Consecutive years -- a Z -- = Rotation pattern not included in study year. Y Means in each column that are followed by the same letter are not significantly different (P<.). Figure. Previous crop impacts peanut yield. Yield (lb/) Yield (lb/) Yield (lb/) Yield (lb/) Yield (lb/) C Yield (lb/) Yield (lb/) Yield (lb/)

8 Previous crop impacted peanut yield in five of seven study years (Figure ). cropped behind corn and cotton yielded significantly higher in four and three years, respectively, when compared with peanut behind peanut. With the exception of, yield response of peanut cropped behind cotton and corn did not significantly differ. - s was noted on cotton, root knot juveniles were often recovered from the plots cropped to corn (Table ). The root knot nematode species was Meloidogyne incognita Race (southern root knot) and not M. incognita Race (cotton root knot), which is an aggressive root parasite of corn and cotton. The plot to plot variation of juvenile counts is associated with differing populations of the smallflower morningglory (Jacquemontia tamnifolia) host of M. incognita Race. From to, cropping frequency had no impact on corn yield (Table ). During that time period, yields were similar for corn cropped for two up to five consecutive years as compared with corn cropped after at least one year of cotton or peanut. eginning in, higher yields were observed for corn following at least one year of cotton or peanut than six or more years of corn monoculture. The yield decline for the corn monoculture as compared with other corn cropping patterns, including two and three consecutive years of corn, was most noticeable in and. With the exception of the corn monoculture after, yield for the remaining corn cropping patterns did not greatly differ. Table : Impact of cropping frequency on root knot juvenile counts and corn yield. cropping frequency Root knot juvenile counts Z Every year (+ years) -- Y -- a ab a bc b Every nd year a X b a b a c a Every rd year -- b a Every th year a a Consecutive years a b -- a a a a Consecutive years -- a a ab a Yield (bu/) Every year (+ years) -- Y -- a a c b c Every nd year a a a a ab a a Every rd year -- a a Every th year a a Consecutive years a a -- a bc a ab Consecutive years -- a a a ab Z Number of juveniles of the southern root knot nematode (M. incognita Race ) per cc of soil recovered. Y -- = Rotation pattern not included in study year. X Means in each column that are followed by the same letter are not significantly different according to Fisher s least significant difference test (P<.).

9 Prior to, previous crop did not have a significant impact on the yield of the successive corn crop (Figure ). From through, yield was higher for corn cropped behind peanut as compared with corn. Higher yield was also noted in and but not for corn following cotton. Previous crop did significantly influence root knot nematode juvenile counts on the following corn crop (data not shown). In five of eight years, lower root knot juvenile counts were recorded in corn following peanut as compared with corn. Typically, root knot nematode juvenile counts in corn cropped behind cotton and corn were similar and often higher when compared with peanut. s previously noted, higher root knot juvenile populations were associated with morningglory, which infested drying corn just prior to harvest. Figure : Influence of previous crop on the yield of corn, -. Yield (bu/) Yield (bu/) Yield (bu/) Yield (bu/) Yield (bu/) Yield (bu/) Yield (bu/) Yield (bu/) SUMMRY Cropping frequency impact on yield was greatest for peanut and to a lesser extent corn but not cotton. Lowest yields were noted in the peanut and corn monoculture in,, and. In peanut, declining yields, which were evident when peanut followed peanut, were closely mirrored by increasing leaf spot intensity. Occurrence of other peanut diseases such as TSWV (data not shown) and stem rot was not as closely tied to peanut cropping frequency. The peanut root knot nematode (M. arenaria Race ) never became established at this location in peanut and populations of Meloidogyne incognita Race remained low regardless of peanut cropping frequency. While no increase in diseases, plant parasitic nematodes, or other pest systems were noted, a sharp decline in yield was noted for the corn monoculture when compared with other cropping patterns that included the peanut and cotton rotation partners. In contrast to corn and particularly peanut, similar yields that were noted across all cotton cropping patterns was due in large part to the absence of the

10 damaging populations of the cotton root knot or reniform nematode as well as damaging disease. s is the case with cropping frequency, previous crop significantly impacted root knot nematode populations and yield of corn as well as TSWV and stem rot incidence, leaf spot intensity, and yield of peanut. In contrast, previous crop had little or no influence on root knot populations on cotton and peanut along with yield of the latter crop. Results confirm previous observations that corn and cotton, neither of which share yield robbing diseases or nematodes with peanut, are equally valuable rotation partners with the latter crop. With few exceptions, similar reductions in leaf spot intensity and to a lesser extent TSWV and stem rot intensity along with up to % higher yields were obtained for peanut cropped behind corn or cotton. While the influence of previous crop as well as peanut cropping frequency on has not previously been observed, planting date, seeding rate, cultivar selection, and row spacing have been shown to influence TSWV levels in peanut. Despite moderate stem rot pressure in several study years, previous crop had very limited impact on stem rot intensity. While yield response for corn cropped behind corn was comparable for four years to those obtained with the cotton and peanut rotation partners, a to % yield reduction for corn after corn was noted in the latter study years. The yield decline noted for corn behind corn as compared with cotton or peanut was not associated with an increase in disease or nematode activity. The same corn variety Pioneer - was planted in all study years. Cotton yield was not greatly affected by previous crop. With one exception, similar lint yields were obtained whether corn, cotton, or peanut was previously cropped. lso, higher disease or nematode activity was not observed in cotton cropped behind cotton as compared with corn and peanut.