Crop Report – Week of July 15, 2024

Corn Pests to Watch for Over the Next Month

Tracey Baute, Entomologist – Field Crops, OMAFA

Corn Rootworm

Like many other pests, corn rootworm (CRW) is ahead of schedule this year. Adult beetles will be emerging this week or next. Anyone considering trapping for adults as part of the Corn Rootworm Trap Network should be setting up their trap sites soon. Monitoring for CRW adults using sticky traps is an effective tool for flagging fields that have suspected Bt resistant rootworm populations if placed in fields planted with a CRW Bt hybrid. The traps can also provide insight into what the risk of rootworm injury will be in next year’s corn crop if that field is in continuous corn production. Higher beetle populations this year mean more eggs being laid in the soil that will hatch into larvae next spring. If sticky traps catch an average of 2 or more beetles per trap per day or if easier – if after 7 days in the field, each of the 4 traps monitored catch 14 or more beetles – that field is at high risk (Figure 1). If these traps are in a field that was planted with a CRW Bt hybrid, this indicates that a lot of rootworms survived feeding on roots expressing Bt and could be a resistant population. These fields need to be reported to your seed provider and myself to test for potential resistance. If the field is not planted to a CRW Bt hybrid but will be going into corn again next year, it will need some form of protection at planting, either by using a soil applied insecticide, planting a CRW Bt hybrid or consider rotating that field out of corn next year to avoid rootworm injury. Crop rotation at least once every 4 years is also a more sustainable management practice to help address resistant rootworm populations. More information on trapping instructions can be found in this Field Crop News Article: https://fieldcropnews.com/2024/06/corn-rootworm-trap-participants-needed/

Figure 1. Corn rootworm sticky trap with beetle capture with more than 2 Beetles per Trap per Day, indicating a high-risk field.

Western Bean Cutworm

Western bean cutworm (WBC) moth flight has begun with a few traps are catching lower levels of moths. Don’t assume low moth counts this early means low risk. With such variable planting dates and growth stages in every region, these early moths may unload a lot of eggs in only a few of the more advanced fields out of desperation. Scouting is advised in the earliest planted fields to check for egg masses. If 5% of the plants scouted over three scouting periods has egg masses, the field will need an insecticide application (Figure 2). Remember that WBC larvae need at least a tassel developing in the whorl to survive in the absence of an ear of corn, so focus on fields in later growth stages first. Fields younger than V8 are less at risk right now. Later planted fields will be at higher risk when peak moth flight takes place late July to early August. More information on moth counts can be found on the Great Lakes and Maritimes Pest Monitoring Network.

Figure 2. Western bean cutworm egg masses (close to hatching – upper; freshly laid – lower) on late V stage corn.

European Corn Borer

With European corn borer (ECB) populations becoming less susceptible to Bt corn, we need to start scouting for unexpected injury in Bt corn. Eastern Ontario needs to be extra vigilant as they neighbour provinces with known resistant populations but all growers in Ontario should start this practice. Scout between 10 to 20 areas of the field after V6 stage, looking for signs of ECB injury including leaf or whorl feeding, frass and stalk tunneling in the midrib or at the leaf axils (Figure 3), bent or broken stalks and the tell-tale sign broken tassels. Any signs of of ECB feeding injury in Bt fields should be reported to your seed provider and myself. Don’t assume the injury you see if on only refuge plants. To help reduce the spread of resistance, shredding stalks during or shortly after harvest will need to become standard practice again to kill any overwintering ECB larvae in the corn stubble left after harvest. More information on recent resistance detections and signs of ECB injury can be found on the Canadian Corn Pest Coalition Website.

More information on biology and management of any of these pests can also be found on Ontario CropIPM and Crop Protection Hub. As always, critical pest updates will also be available through the rest of the season on Field Crop News.

Figure 3. European corn borer stalk tunneling and frass at leaf axil. Photo credit: Dr. Jocelyn Smith, University of Guelph Ridgetown Campus.

Weather Summary: Thursday, July 11 to Wednesday, July 17 2024

Location	Highest Temp (°C)	Lowest Temp (°C)	Rain for Week (mm)	Rain Since April 1st (mm)	GDD0C April 1st	GDD5C April 1st	CHU May 1st
HARROW
2024	29.2	17.2	10.2	318.7	1867	1330	1870
2023	28.6	15.5	30.0	272.5	1646	1122	1631
2022	29.8	12.8	59.9	279.9	1689	1183	1754
10 YR Norm (11-20)	29.1	17.0	11.9	341.4	1701	1163	1782
RIDGETOWN
2024	29.0	14.7	44.1	431.5	1763	1230	1759
2023	28.0	14.2	20.1	343.4	1561	1046	1517
2022	29.3	9.6	22.6	203.9	1575	1076	1603
10 YR Norm (11-20)	28.8	15.3	18.4	284.6	1598	1063	1659
SARNIA
2024	30.5	14.4	82.5	373.7	1744	1213	1713
2023	30.0	14.7	38.8	246.7	1515	1001	1430
2022	30.5	11.1	11.6	176.8	1555	1062	1547
10 YR Norm (11-20)	30.0	16.4	13.3	303.5	1553	1021	1603
LONDON
2024	29.8	15.5	108.2	463.0	1736	1201	1740
2023	27.8	13.1	29.4	314.7	1554	1039	1512
2022	29.2	9.7	5.5	200.7	1530	1040	1560
10 YR Norm (11-20)	29.5	15.2	14.9	306.4	1575	1044	1637
BRANTFORD
2024	29.7	15.7	89.0	389.8	1680	1149	1689
2023	27.7	13.2	15.5	268.8	1545	1029	1506
2022	30.2	8.4	14.3	200.3	1532	1031	1520
WELLAND
2024	29.2	16.5	23.4	391.6	1742	1207	1768
2023	27.4	14.1	23.1	268.1	1558	1037	1513
2022	29.8	11.6	11.9	204.4	1580	1071	1609
10 YR Norm (11-20)	28.5	16.2	10.2	291.4	1580	1048	1643
GODERICH
2024	27.9	13.9	21.0	261.5	1568	1041	1553
2023	25.7	10.3	53.9	209.5	1419	921	1357
2022	28.6	8.2	13.4	164.0	1419	931	1412
10 YR Norm (11-20)	27.4	15.1	9.4	251.2	1417	895	1459
ELORA
2024	27.9	13.8	39.6	341.9	1565	1042	1579
2023	26.6	10.0	51.0	255.7	1426	926	1380
2022	28.4	7.1	1.6	179.0	1399	910	1389
10 YR Norm (11-20)	28.0	13.3	15.7	305.9	1412	894	1455
MOUNT FOREST
2024	27.8	13.6	24.9	329.8	1550	1030	1564
2023	25.8	10.3	39.1	282.8	1422	926	1378
2022	28.4	8.8	12.2	206.4	1399	918	1407
10 YR Norm (11-20)	27.5	13.5	14.4	299.5	1393	883	1450
BARRIE
2024	28.2	14.3	10.4	496.7	1510	990	1537
2023	27.5	11.0	67.8	351.2	1409	907	1368
2022	29.7	10.1	4.6	225.1	1371	879	1378
10 YR Norm (11-20)	27.6	13.5	13.3	274.6	1373	865	1425
PETERBOROUGH
2024	29.6	13.6	29.5	346.6	1551	1027	1551
2023	29.2	9.5	59.6	254.3	1453	941	1377
2022	29.1	9.2	9.4	227.5	1413	911	1419
10 YR Norm (11-20)	28.9	12.9	14.0	272.2	1431	912	1461
KEMPTVILLE
2024	31.0	17.0	13.3	375.2	1637	1114	1683
2023	31.0	13.2	48.4	286.9	1555	1048	1493
2022	30.6	11.1	32.5	345.5	1513	993	1530
10 YR Norm (11-20)	28.8	14.4	14.9	297.5	1501	984	1555
SUDBURY
2024	29.0	13.0	9.8	378.4	1394	897	1440
2023	24.8	10.4	21.2	361.6	1337	874	1335
2022	27.5	9.8	3.0	210.8	1259	796	1310
10 YR Norm (11-20)	26.6	12.7	17.1	280.7	1267	808	1357
EARLTON
2024	30.4	11.0	7.3	335.3	1379	889	1428
2023	26.3	9.7	14.5	246.8	1324	859	1321
2022	29.8	7.1	8.5	208.5	1257	803	1309
10 YR Norm (11-20)	27.2	11.8	16.1	251.3	1179	743	1269
SAULT STE MARIE
2024	26.4	11.3	10.3	374.3	1269	758	1237
2023	25.4	9.9	9.5	220.4	1266	800	1220
2022	24.3	8.4	5.9	249.9	1069	610	1024
10 YR Norm (11-20)	26.7	9.5	13.0	279.3	1129	672	1152
THUNDER BAY
2024	31.6	7.6	31.0	277.5	1176	687	1140
2023	26.3	6.0	6.0	185.8	1153	710	1177
2022	27.9	5.7	5.5	363.8	1046	620	1056
10 YR Norm (11-20)	26.0	11.0	24.7	286.9	1096	648	1137
FORT FRANCES
2024	30.4	7.3	28.9	338.8	1238	738	1231
2023	25.7	6.0	7.4	197.9	1315	866	1375
2022	30.8	11.0	32.1	474.7	1128	704	1203
10 YR Norm (11-20)	27.5	12.3	23.0	276.1	1222	756	1297