An early prediction of crop biomass at maturity and yield is important in different circumstances. The use of spectral reflectance indices, such as the Normalized Difference Vegetation Index (NDVI), has been proposed as a fast, nondestructive way of estimating crop growth capacity. In this study, we examined whether NDVI assessment relatively early in the crop cycle may be useful for predicting final biomass and yield in wheat. To that end, NDVI was measured and biomass quantified regularly from tillering to maturity for six different wheat genotypes grown under a contrasting range of N and water availabilities. In addition, final biomass and yield were measured at maturity. In line with expectations from the literature, we found that NDVI at milk-grain stage was well correlated to final yield and biomass. However, it was also observed that NDVI at the onset of stem elongation was also reasonably correlated to both attributes. Because crop growth in wheat from the end of tillering to anthesis is related to the determination of grain number and yield, we propose the use of NDVI at the onset of stem elongation as a complementary criterion for establishing the required late crop management (N fertilisation, irrigation) practices.

Waterlogging, if occurring within the stem elongation period (SE), is particularly critical for yield determination. We quantified for the first time the effect of waterlogging duration during SE on yield and studied whether the effects were only direct on resource capture or whether there were feed-forward effects as well. We grew wheat (cv. Soissons) outdoors in long tubes (1.25 m deep) forming a normal canopy and imposed different treatments in SE to finish simultaneously around anthesis (0, 4, 8, 12, 16, 20 and 24 days) plus two complementary treatments (8 and 16 days) starting 10 days after the onset of SE. Yield was reduced linearly with the duration of waterlogging c. 2 % d waterlogging À1 . Treatments mainly affected pre-anthesis spike growth reducing the number of fertile florets and grains, not affecting fruiting efficiency. The magnitude of grain number loss was inversely proportional to the hierarchy of the spikes and spikelets. Grain weight was more marginally reduced, likely through the effects on the size of the ovaries of the developing florets. This reveals a direct effect of waterlogging on the capture of resources with no major feed-forward effects. Losses were in agreement with those from other studies for particular durations of waterlogging.

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The potential of azadirachtin as an insect growth regulator was evaluated in Nezara viridula L. by applying different doses to fifth instar nymphs. At doses of 200-500 ng per insect almost all the individuals died during moulting to adults and the survivors showed a great number of nymphal characteristics, and also died very soon after. At lower doses, from 2 to 50 ng per insect, approximately 50% of the adults seemed normal. No effect was observed during the last nymphal instar, even at the highest dose applied. The fertility and fecundity of adults, males and females, developing from nymphs treated with different low doses of azadirachtin were also studied. When azadirachtin was applied at 20 ng per insect on fifth instar nymphs, females developing from these nymphs showed a conspicuous reduction of fecundity. This same effect was evident when untreated females mated with males obtained from treated nymphs. Finally, azadirachtin applied at 1 lg ⁄ cm 2 to the oviposition surface showed a remarkable oviposition repellency. Materials and methods Insect rearingNezara viridula was reared according to the procedure of Harris and Todd (1981) at 25±1°C and 16 h light : 8 h dark. The adults and the nymphs were fed a diet that was replaced weekly, consisting of fresh green beans, washed carefully with water, and dried before use, and of raw and peeled peanuts. Adults collected from different fields of Lleida province (north-east Spain) were placed in rearing boxes (transparent plastic cylindrical pots, 17 cm · 10 cm), with the bottom covered with filter paper, that was changed periodically, and the top perforated and covered by mosquito net. A 3 cm · 17 cm strip of glossy paper, on which the females deposited their eggs on the interior side, was hung diagonally JEN 127 (2003)