Effects of D-D, Telone or dazomet applied to potato ridges in spring on potato cyst-nematode, Heterodera rostochiensis, in sandy loam and silt loam soils

Large amounts of dazomet (329, 439 kg/ha) applied to potato ridge soil in spring, before potatoes were planted, controlled potato cyst-nematode (Heterodera rostochiensis) in sandy loam and silt loam more effectively than large amounts of D-D (359, 448 kg/ha). In heavily infested sandy loam, 329 kg dazomet/ha or 857 kg methyl bromide/ha applied in spring 1969 or 439 kg dazomet/ha applied in autumn 1968, greatly decreased the number of larvae able to invade potato roots, so Majestic potatoes grew and yielded well without increasing the number of nematodes left in the soil after harvest. Large amounts of D-D or Telone applied to the topsoil in autumn or to the ridges in spring were less effective in controlling potato cyst-nematode or increasing potato yields. Applied in spring 1969 to silt loam ridges, 439 kg dazomet/ha had more effect than 448 kg D-D/ha on potato cyst-nematode and on the increase in yield of Majestic potato. The yield of Maris Piper potatoes (resistant to H. rostochiensis pathotype A) in infested silt loam was increased greatly by D-D, as much by 112 as by 224 or 448 kg/ha.     

Control of potato cyst-nematode, Heterodera rostochiensis, in sandy, peaty and silt loam soils by dazomet and Telone applied in different ways

Dazomet applied in the ridges in autumn or in spring, before potatoes were planted in them, controlled potato cyst-nematode (Heterodera rostochiensis), British pathotype A, better in sandy loam and peaty loam than Telone (1,3-dichloropropene mixture). In sandy loam dazomet controlled potato cyst-nematode as well when applied in spring as when applied in autumn and as well when the soil was ridged after treatment as when it was not. Telone was as effective when applied to ridges in autumn as when applied to ridges in spring. In peaty loam potato cyst-nematodes were least abundant after a crop of Maris Piper potatoes. The yields of King Edward potatoes were greatly increased and nematode multiplication was greatly reduced by dazomet incorporated in the ridges in autumn. Two equal doses of dazomet, one incorporated in the topsoil before, the other after ploughing, controlled potato cyst-nematode as well and increased the yield of King Edward potatoes more than an equivalent amount of dazomet applied after ploughing. Dazomet applied to silt loam soil in two dressings, one before, the other after, ploughing, controlled potato cyst-nematode better than an equal amount applied as a single dressing after ploughing. The nematode was controlled best by two large dressings of dazomet or by a combined treatment of dazomet and Telone.     

Control of potato cyst-nematode, Heterodera rostochiensis, in peaty loam soil by D-D, aldicarb and a resistant variety of potato

In peaty loam soil in Cambridgeshire, 5.2 or 10.3 kg aldicarb/ha incorporated in the top-soil before potatoes were planted controlled potato cystnematode (Heterodera rostochiensis Woll.) better than 384, 769 or 1153 kg D-D/ha injected 15 cm deep into the top-soil in the preceding autumn. 10.3 kg aldicarb/ha applied in 1968 and 1969 permitted King Edward potatoes (susceptible to H. rostochiensis) to grow well in infested soil and prevented multiplication of pathotypes of H. rostochiensis on Maris Piper potatoes (resistant to H. rostochiensis pathotype A). Although large amounts of D-D applied in 1968 and 1969 increased the yield of King Edward potatoes in both years they did not control potato cyst-nematode in the second year.     

Incorporating granular nematicides in soil to control potato cyst-nematode, Heterodera rostochiensis

Incorporating either Du Pont 1410 or Nemacur P at 11-2 kg a.i./ha in peaty loam topsoil in Spring, controlled potato cyst-nematodes (Heterodera rostochiensis) to 20 cm deep as well as did 5.6 kg incorporated in Winter before ploughing followed by another dose of 5.6 kg incorporated in the seedbed in Spring. In pots Du Pont 1410 remained effective after several months incubation in soil at 5 or 10 ^oC. Dazomet at 440 kg/ha incorporated in the topsoil in Winter (220 kg before ploughing and 220 kg after ploughing) did not control the nematodes as consistently as 5.6 or 11.2 kg a.i./ha of Du Pont 141 o or Nemacur P, even when the dazomet-treated plots were covered with Polythene sheeting to prolong fumigation. In large containers, aldicarb at 45 mg a.i./13 l soil increased the yield of Arran Banner potatoes as much when incorporated to 13 cm deep in moderately infested peaty loam as when incorporated to 25 or 38 cm deep, but not as much as when all the soil (to 51 cm deep) was treated. Treating the soil to 13 cm deep did not control the nematodes 13–25 cm deep even though some of the nematicide was probably leached into this layer. In field plots, the nematodes were better controlled when Du Pont 1410 or Dowco 275 was rotavated into the top 10 cm than into the top 20 cm of a peaty loam soil. Rotavating soil twice instead of once after applying aldicarb, Du Pont 1410 or Dowco 275 to the soil surface did not increase nematode control. Although small amounts of aldicarb incorporated into the topsoil in Spring controlled the nematodes, the same amounts concentrated in the seed furrows, just before susceptible potatoes were planted in them, did not.     

Control of potato cyst-nematode, Heterodera rostochiensis, in three soils by small amounts of aldicarb, Du Pont 1410 or Nemacur applied to the soil at planting time

Aldicarb or Du Pont 1410 (S-methyl 1-(dimethylcarbamoyl)-N-[(methylcarbamoyl) oxy] thioformimidate) at 2.6–11.2 kg a.i./ha applied to the soil at planting time controlled potato cyst-nematode, Heterodera rostochiensis, in sandy loam, peaty loam and silt loam and greatly increased tuber yields of susceptible potatoes. Nemacur (O-ethyl-O-(3-methyl-4-methylthiophenyl) isopropylamido-phosphate) controlled potato cyst-nematode in sandy loam at 2.9–10.3 kg a.i./ha and in silt loam at 11.2 kg a.i./ha but did not control the nematode well in peaty loam even at 22.4 kg a.i./ha. In peaty loam aldicarb and Nemacur were more effectively incorporated by rotavation than by a modified power harrow.     

Chemical control of potato cyst-nematode in sandy clay soil

In sandy clay soil in Bedfordshire, potato cyst-nematode (Heterodera rostochiensis Woll.) was controlled and yields of Majestic potatoes greatly increased when i-2g aldicarb, 4-0 g fensulphothion or 10-3 g diazinon, disulphoton, ‘Isolan’ (i-isopropyl-3-methyl-5-pyrazolyl dimethylcarba-mate) or thionazin per m² were incorporated in the top soil before potatoes were planted. Diethyl phosphorothioates controlled H. rostochiensis better than dimethyl phosphates. One hundred and eleven g methyl bromide, 47-6 g carbon disulphide or 45-2 g D-D per m² applied to the soil and covered with polyethylene sheeting greatly increased the yield of potatoes, but also increased the number of nematodes in the soil. Estimates of the number of larvae able to invade potato roots in treated soil after harvest and of cysts, total eggs or live eggs selected the same range of treatments as effective in controlling H. rostochiensis.     

Chemical control of beet cyst-nematode, Heterodera schachtii, in some peaty loam soils

In peaty loam soils, aldicarb or oxamyl mixed with the top 15 cm of the soil in spring before sugar beet seeds were sown, minimised invasion of the roots by larvae of the beet cyst-nematode, Heterodera schachtii, so preventing injury to the seedlings, and greatly increased sugar yields in heavily infested soil. Small amounts of both compounds were often as effective as larger amounts. Nematode increase on sugar beet roots was slow. Aldicarb or oxamyl lessened nematode increase in four years out of five. Fumigating predetermined row positions with dichloropropene mixtures (D-D, Telone) or incorporating aldicarb or methomyl shallowly in soil, later occupied by the roots of sugar beet seedlings, did not control the nematode, although sugar yields were sometimes increased.     

Effects of rotation length and oxamyl on potato yield and the potato cyst-nematode, Globodera rostochiensis, in a sandy loam soil

In sandy loam infested with golden potato cyst-nematode, Globodera rostochiensis, oxamyl at 5.6 kg a.i. ha^-1 incorporated in the top 15 cm of the soil just before planting potatoes greatly reduced nematode population increase on susceptible cv. Désirée grown six, seven or eight years after the last susceptible potato crop, but did not significantly increase tuber yields. In four-course and two-course rotations, oxamyl also controlled increase of G. rostochiensis and greatly increased yields of both cv. Désirée and resistant cv. Maris Piper. Oxamyl maintained tuber yields in a four-course rotation at the same level as in a six to eight-course rotation. Decline of G. rostochiensis in the soil was much faster under barley in some two-course rotations than under barley in four-course rotations.     

Resistance to the potato cyst-nematode, Heterodera rostochiensis, in the plant genus Lycopersicon

Forty-eight lines of Lycopersicon and four lines of Solanum were screened for resistance to twelve Heterodera rostochiensis populations of known patho-type(s). Plant lines were assessed for resistance first by examining the outside of the root ball for cysts and later by washing the root ball to extract all cysts. Possible resistant plant selections were re-tested against three eelworm populations, including the one to which they were first shown resistant. Resistance was discovered in two lines of Lycopersicon pimpinelli-folium, two L. esculentum L. pimpinellifolium crosses, L. esculentum var. cerasiforme, six lines of L. peruvianum, in L. peruvianum var. humifusum, L. hirsutum var. glabratum, and in Solanum indicum. Because resistance was found most commonly in L. peruvianum and because it has already been used as a resistant parent in breeding programmes to incorporate resistance to root-knot nematode (Meloidogyne spp.) in tomato, L. peruvianum seems to be the best source of resistance among plants tested so far. The host-parasite relationships of resistant L. hirsutum var. glabratum (B 6013) were compared with those of a commercial, susceptible tomato, L. esculentum‘Ailsa Craig’. Plants were inoculated with three eelworm isolates; the extent of eelworm invasion, plant reaction and eelworm development were studied. Larvae invaded and penetrated roots of the resistant plant as freely and in as large numbers as they penetrated roots of the susceptible tomato. In the latter, numerous larvae matured while, in contrast, few larvae matured in the roots of L. hirsutum var. glabratum. L. hirsutum var. glabratum was shown to possess a root diffusate as active in hatching larvae of Heterodera rostochiensis as that of L. esculentum‘Ailsa Craig’. The existence of pathotypes of H. rostochiensis, identifiable by their differing abilities to increase on resistant tomato lines, was not clearly revealed in the experiments.     

Control of potato cyst-nematodes, Heterodera rostochiensis and H. pallida, in sandy, peaty and silt loam soils by oximecarbamate and organophosphate nematicides

Small amounts (5.6 or n-2 kg a.i./ha) of aldicarb or oxamyl, incorporated in the soil before potatoes were planted in spring, controlled potato cyst-nematodes (Heterodera rostochiensis and H. pallida) on susceptible cultivars equally well in sandy, peaty and silt loam soils. In soils treated with either nematicide, nematode numbers increased little or decreased; in untreated soils nematode numbers increased greatly. In contrast organophosphate nematicides, similarly applied, fenamiphos (proposed BSI common name for O-ethyl-O-(3-methyl-4-methylthiophenyI)-isopropylamido-phosphate), ethoprophos (proposed BSI common name for (O-ethyl S, 5-dipropyl phos-phorodithioate), CGA 12223 (O, O-diethyl O-[i-isopropyl-5-chloro-i,2,4-triazoIyl-(3)] phosphorothioate) and Dowco 275 (O, O-diethyl O-(6-fluoro-2 pyridyl) phosphorothioate), were ineffective at one or more of the experimental sites. Potato yields were greatly increased by oximecarbamate or organophosphate nematicides only in soils heavily infested with the nematodes.     

Control of potato cyst-nematode, Heterodera rostochiensis, in silt and peat loams by ten pesticides applied to the soil at planting time

Incorporated in silt or peat loam top-soil in spring before susceptible potatoes were planted, three carbamoyl oximes, aldicarb, Tirpate (2,4-dimethyl-2-formyl 1-1,3-dithiolane oxime iV-methylcarbamate) and Du Pont 1410 (S-methyl i-(dimethylcarbamoyl)-N-((methylcarbamoyl) oxy) thioformimidate) and one organophosphate, Nemacur (O-ethyl-O-(3-methyl-4-methylthiophenyl)-isopropylamidophosphate) all at n-2 kg a.i./ha greatly increased the yield of tubers and effectively controlled potato cyst-nematode (Heterodera rostochiensis Woll.). At the same dosage thionazin was as effective in the peat loam but was ineffective in the silt loam; phorate and Mocap (O-ethyl S,S-dipropyl phosphorodithioate) were less effective and chlorfenvinphos, diazinon and a coarse granule formulation of fensulphothion were ineffective in controlling potato cyst-nematode.     

Control of potato cyst-nematode, Heterodera rostochiensis, in sandy loam, by Du Pont 1410 (S-methyl l-(dimethylcarbamoyl)-N-[(methylcarbamoyl) oxy] thioformimidate) applied to the soil at planting time

When applied to heavily infested sandy loam soil at planting time, as little as 5 ppm Du Pont 1410 (5-methyl I-(dimethylcarbamoyl)-N-[(methylcar-bamoyl) oxy] thioformimidate) in pots, or 2–5 ppm in field plots, effectively controlled potato cyst-nematode, Heterodera rostochiensis Woll., and greatly increased the growth and yield of susceptible potatoes. Dipping the shoots of potted King Edward potatoes once in aqeuous solution containing 2000 ppm did not control potato cyst-nematode. Nematode control was not increased when 2 or 4 kg a.i./ha was sprayed on the foliage of young Pentland Crown potatoes growing in soil already treated with the nematicide.     

Growth and survival of cowpea rhizobia in bauxitic silt loam and sandy clay loam soils

Survival of 4 cowpea Rhizobium strains, IRC291, MI-50A, JRW3 and JRC29, in two soil types (bauxitic silt loam and sandy clay loam) undergoing drying at 30°C and 37°C was examined. While all strains except JRW3 showed a general pattern of increase in their numbers during the first 3 weeks in sterile soils, none of the strains showed any increase in their population in non-sterile soils. Cowpea rhizobia showed better survival in non-sterile bauxitic silt loam than in clay loam soils at 30°C. However, the long-term survival (examined up to 6 months) of rhizobia in both soils was poor at 37°C as compared to 30°C. We also found that cowpea rhizobia survived better in soils undergoing drying than in moist soils at 30°C. Our results suggest that (a) cowpea rhizobia survived better in bauxitic silt loam than in clay loam soil and (b) the low indigenous cowpea rhizobial population in Jamaican soils may be due to their poor long-term survival and weak saprophytic competence.     

The effects of deep cultivation and oxamyl on control of potato cyst-nematode, Globodera rostochiensis

Soil compaction associated with frequent cultivation of potatoes was partly removed with a deep winged-tine coulter. This increased the yield of tubers of cv. Cara in 1987 and 1988 and of cv. Désirée in 1987 in soil which was heavily infested with potato cyst-nematode, Globodera rostochiensis (Woll.), and which was treated with oxamyl at 5.6 kg ha^-1. In 1988, in soil not treated with oxamyl, deep cultivation significantly decreased the yield of cv. Cara. In both years, oxamyl decreased numbers of G. rostochiensis eggs in the soil following cv. Désirée potatoes but not following cv. Cara which were resistant to the nematode.     

Control of potato cyst-nematodes, Globodera rostochiensis and G. pallida, in different soils by small amounts of oxamyl or aldicarb

In eleven field trials on peaty, sandy or silt loam soils, aldicarb or oxamyl, incorporated in the soil to 15 cm deep before susceptible potatoes were planted, controlled potato cyst-nematodes (Globodera rostochiensis (Woll.) Mulvey & Stone, 1976 and G. pallida (Stone) Mulvey & Stone, 1976) better at 5–6 kg than at 3–4 or 2-2 kg a.i./ha. Incorporated in the soil to 7-5 cm deep 5–6 kg/ha of aldicarb or oxamyl controlled the nematodes less effectively at some sites. At 3–4 kg a.i./ha there was no difference in nematode control between the two incorporation depths.     

Association between the potato cyst-nematode, Heterodera rostochiensis Woll., and Verticillium dahliae Kleb. in the early-dying disease of potatoes

Investigation of a possible association between Verticillium dahliae and H. rostochiensis (pathotype E, British notation) was based on field observations and an examination of disease development in single-stemmed potato plants grown in pots. An association was found in the distribution of the nematode and the fungus in the field, and the disease was far more severe with a combined infection than with either pathogen alone. Studies on leaf-area development and yield reduction suggest there is synergism between fungus and nematode, the reductions produced by the combined infection exceeding the sum of those produced by either pathogen alone. Fungal mycelium and the extent of host colonization by V. dahliae were greatly increased by the presence of the nematode. The possible benefits to V. dahliae in the fungus-nematode complex are discussed.     

Control of beet cyst-nematode, Heterodera schachtii, by aldicarb applied to the soil by a vertical band-reciprocating harrow technique or by rotary cultivation

As little as 0.8 kg aldicarb ha^-1 applied to bands of soil 15 cm wide × 15 cm deep, in which sugar beet seeds were sown, increased beet yields as much as did 2.6 or 5.0 kg ha^-1 rotary cultivated into the top 15 cm of soil lightly or moderately infested with beet cyst-nematode, Heterodera schachtii. In a very heavily infested soil, 1.7 kg ha^-1 applied to the bands of soil increased beet yields as much as 2.6 kg ha^-1 rotavated into the top 15 cm of the soil; yields were further increased by 5.0 and 9.9 kg ha^-1 rotavated in but not by 3.5 kg ha^-1 in the bands of soil. Soil populations of the nematode increased little or not at all whether the soil was treated with aldicarb or not. The band treatment was achieved by a vertical band- reciprocating harrow technique, which is described. The advantages of this new technique for the control of beet cyst-nematode and other soil pests of widely spaced row crops are safer application of less pesticide, thereby minimising cost of treatment and any risk to the environment, faster seedbed preparation and adequate control of pest population increase on the susceptible crop, especially if coupled with biological control.     

Incorporation of granular nematicides in soil to control pea cyst-nematode, Heterodera goettingiana

Experiments at four sites in England compared control of pea cyst-nematode, Heterodera goettingiana, on peas, Pisum sativum, obtained when 10% granules of aldicarb or oxamyl were applied to the soil in different ways. The nematode was controlled best when the granules were incorporated in the soil by rotary cultivation (L-bladed rotavator). The granules were incorporated too shallowly by rotary harrowing (Lely Roterra); applying granules in the seed furrows during sowing, or broadcasting them at the sowing depth of 5 cm, was only effective in 1975 when heavy and prolonged rain followed sowing.     

The population genetics of the potato cyst-nematode, Heterodera rostochiensis: mathematical models to simulate the effects of growing eelworm -resistant potatoes bred from Solatium tuberosum ssp. andigena

To follow population changes when potato varieties with resistance to Heterodera rostochiensis derived from Solanum tuberosum ssp. andigena were grown on infested land, a computer programme was written including three mathematical relationships: (1) a law relating multiplication to pre-cropping density; (2) two mathematical models of inheritance of ability to overcome resistance; (3) a law relating the proportion of larvae able to become female to pre-cropping population density. The programme also included four parameters: (1) the maximum possible reproductive rate; (2) the fraction of the population (eggs) not participating in reproduction when potatoes are grown and carried over to the following year unchanged; (3) the fraction carried over annually when other crops are grown; (4) the frequency of larvae able to become female in the population initially. Population density was measured relative to the equilibrium density and was therefore independent of the units in which density is usually measured. After supplying a range of parameters for all the above to include those likely to be encountered in practice, the changes expected (a) in the frequency of larvae able to become female in the roots of resistant varieties and (b) in population density were computed for resistant varieties grown continuously or alternately with susceptible varieties in crop rotations of different lengths. Because well established field populations are relatively dense, observed reproductive rates are small and rarely approach the maximum possible. Reproductive rate is therefore a relatively unimportant determinant of genetic change. The fraction of the population carried over to the following year is more important because it affects the length of a crop rotation necessary to make loss of potato yield acceptable, determines what the multiplication rate will be and influences the speed of genetic change by providing a reservoir of initial type males which backcross with any genetically different females that may develop on the roots of resistant plants. No experiment seems to have been done specifically to determine the parameters needed to calculate population changes. Some values can be obtained from the literature but mostly they must be guessed. When the law relating the proportion of larvae able to become female to pre-cropping population density was included in the computations, it had little effect initially but later, after several generations, it delayed genetic change. Two field experiments, one by Huijsman (1961) another by Williams (1958) and Cole & Howard (1962 a), provide some of the variables needed to compute trends in population density. Best fitting variables were computed for the data in these experiments by the method of maximum likelihood. The computed parameters for one experiment were not very realistic but those for the other were in line with what would be expected in practice and tended to favour the hypothesis that larvae able to become female in the roots of resistant plants are double recessives (aa). The computations lead us to suggest that the best policy for potato growers who have fields suitable for resistant varieties is to alternate resistant with susceptible varieties in a crop rotation containing potatoes every 3 or 4 years.     

Control of pea cyst-nematode, Heterodera goettingiana, by small amounts of aldicarb, Du Pont 1410, Ciba-Geigy 10576 or Dowco 275 applied to the soil at planting time

Aldicarb, or Du Pont 1410 (S-methyl-I-(dimethylcarbamoyl)-N-[(methyl-carbamoyl)oxy]thioformimidate), at 2.8–22.4 kg a.i./ha incorporated in the seed-bed before sowing greatly increased the yield of peas in a clay loam and two sandy clay soils infested with pea cyst-nematode, Heterodera goettingiana, and lessened or prevented increase in the number of nematodes. CibaGeigy 10576 (an organophosphorus compound) at 5.6–22.4 kg a.i./ha was similarly effective in a sandy clay soil. Dowco 275 (O, O-diethylO-(6-fluoro-2 pyridyl) phosphorothioate) at 5.6 or 11.2 kg a.i./ha also controlled the nematode well in the clay loam and in a sandy clay soil but although it greatly increased the yield of peas in the clay loam, it did not increase yield in the sandy clay.