The variability in crop growth stages was one of the topics emphasised at the Teagasc Kildare field walk last week. On what turned out to be a not-so-nice evening, there was still an opportunity to get out into the fields to see crops, and wheat varieties in particular.

Most varieties are now either side of GS32, or the third-last leaf emerged, but nationally they range from GS30 to GS38/39 on rapidly developing varieties such as Cellule. This could be seen in the height variation on the night, with Cellule the bones of 50cm tall and still growing. The crop in Kildare sown on 10 October was at GS37, with the flag leaf just beginning to peep through.

The visit took place on the farm of Philip and Helen Harris, who farm near Clane. Adviser Ivan Whitten and tillage specialist Shay Phelan explained the general differences between some of the varieties, which varied from GS32 to GS37 in the same field with the same sowing date. This is especially important for the start of disease control, which should begin once the third-last leaf is fully emerged and preferably unfolded on main stems.

This stage was continuously emphasised because it is the best timing to begin to protect the three top leaves on wheat, which are so important for the delivery of yield. Individual varieties differed in this regard but most crops and varieties were at GS32 with the third-last leaf emerged and so at the timing for the first fungicide application. Indeed, most had been sprayed recently with either Jenton plus Venture Extra plus Bravo (where yellow rust was an issue) or Velogy Era (similar to Elatus Era but with slightly higher prothioconazole content) plus Bravo.

The varieties seen included JB Diego, Costello, Graham, and Bennington. The Bennington and JB Diego showed signs of yellow rust but Bennington also showed considerable but irregular scorch symptoms, which were so common this spring. The crop showed yellow patches and circles which one would more normally associate with yellow rust. However, the worst of the damage was more likely associated with spray damage due to the general appearance of the damage and that fact that there were so few lesions visible.

Paint spray to crosscheck

Two weeks before we visited, Helen had sprayed a small square of wheat with white aerosol paint spray. This is described as a very useful technique for any grower to monitor where spray might be placed relative to leaf emergence at the time. It is also a useful way to monitor growth and leaf emergence. On the night, what had been sprayed two week earlier at around GS31 was almost green again as the new leaves emerged and grew up through the painted canopy. Shay stated that doing that on the day one sprays is a great record of the actual stage of the crop at the time of spraying.

He also emphasised the dual importance of having the third-last leaf emerged at the time of spraying. Having this right means that the interval and timing of the next fungicide at GS39 is far more likely to fit cleanly in the programme. Both leaf emergence and the development of septoria are temperature related and because leaves come faster, the timing of the T2 fungicide works well.

However, if the T1 fungicide was applied much earlier than the recommended timing, the advice must be apply an additional contact fungicide one to two weeks after the initial T1 spray. The objective must always be to protect the top three grain-filling leaves.

Winter barley patches

The most forward winter barley in the area now has the flag leaf fully emerged while awns are just visible on the most forward crops elsewhere in the country. But Ivan Whitten said that there is considerable height variability within crops. While there are yellow leaves present, the height is highly unlikely to be a consequence of dwarfing from BYDV infection.

Louise Mc Namara from Teagasc Oak Park was also on hand and there was a very interesting discussion on BYDV control in the absence of Redigo Deter next autumn. Louise told us the most recent research conducted largely verified the recommendation generated over two decades ago in that the optimum timing on later-sown spring crops is GS14 (four leaves) while early autumn sown will mean two aphicides with crops sown in the second half of October best treated with a single aphicide.

While yellow leaves are still likely in treated crops, Louise commented that it is virtually impossible to prevent these and generally not economical to try to do so except in extraordinary conditions. However, with some aphid populations now carrying a number of different resistance mechanisms, control cannot be taken for granted. This means that continuous monitoring will be essential and that all possible non-chemical control methods must be used also.